Method and device for transmitting and receiving PPDU on basis of FDD in wireless LAN system

ABSTRACT

A method and a device for transmitting and receiving a PPDU on the basis of an FDD in a wireless LAN system are presented. Particularly, an AP transmits a trigger frame to a first STA and a second STA. The AP transmits a first downlink (DL) PPDU to the first STA on the basis of the trigger frame. The AP transmits a second DL PPDU to the second STA on the basis of the trigger frame. The AP receives a first uplink (UL) PPDU from the second STA on the basis of the trigger frame. The trigger frame includes bandwidth information of a primary channel and a secondary channel. The first DL PPDU is transmitted through the primary channel. The second DL PPDU and the first UL PPDU are transmitted through the secondary channel. The first and second DL PPDU are simultaneously transmitted. The first UL PPDU is received after a preset period after the second DL PPDU is transmitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2019/006205, filed on May 23, 2019,which claims the benefit of earlier filing date and right of priority toKorean Application No. 10-2018-0058191, filed on May 23, 2018, thecontents of which are all hereby incorporated by reference herein intheir entirety.

BACKGROUND Field

The present specification relates to a scheme of performing frequencydivision duplex (FDD) in a wireless local area network (WLAN) system,and more particularly, to a method and apparatus for transmitting andreceiving a physical layer protocol data unit (PPDU) by using the FDDscheme in the WLAN system.

Related Art

Discussion for a next-generation wireless local area network (WLAN) isin progress. In the next-generation WLAN, an object is to 1) improve aninstitute of electronic and electronics engineers (IEEE) 802.11 physical(PHY) layer and a medium access control (MAC) layer in bands of 2.4 GHzand 5 GHz, 2) increase spectrum efficiency and area throughput, 3)improve performance in actual indoor and outdoor environments such as anenvironment in which an interference source exists, a denseheterogeneous network environment, and an environment in which a highuser load exists, and the like.

An environment which is primarily considered in the next-generation WLANis a dense environment in which access points (APs) and stations (STAs)are a lot and under the dense environment, improvement of the spectrumefficiency and the area throughput is discussed. Further, in thenext-generation WLAN, in addition to the indoor environment, in theoutdoor environment which is not considerably considered in the existingWLAN, substantial performance improvement is concerned.

In detail, scenarios such as wireless office, smart home, stadium,Hotspot, and building/apartment are largely concerned in thenext-generation WLAN and discussion about improvement of systemperformance in a dense environment in which the APs and the STAs are alot is performed based on the corresponding scenarios.

In the next-generation WLAN, improvement of system performance in anoverlapping basic service set (OBSS) environment and improvement ofoutdoor environment performance, and cellular offloading are anticipatedto be actively discussed rather than improvement of single linkperformance in one basic service set (BSS). Directionality of thenext-generation means that the next-generation WLAN gradually has atechnical scope similar to mobile communication. When a situation isconsidered, in which the mobile communication and the WLAN technologyhave been discussed in a small cell and a direct-to-direct (D2D)communication area in recent years, technical and business convergenceof the next-generation WLAN and the mobile communication is predicted tobe further active.

SUMMARY

The present specification proposes a method and apparatus fortransmitting and receiving a physical layer protocol data unit (PPDU),based on frequency division duplex (FDD), in a wireless local areanetwork (WLAN) system.

An example of the present specification proposes a method oftransmitting and receiving a PPDU, based on FDD.

The present embodiment may be performed in a network environment inwhich a next-generation WLAN system is supported. The next-generationWLAN system is a WLAN system evolved from an 802.11ax system, and maysatisfy backward compatibility with the 802.11ax system.

The present embodiment may be performed in a transmitting device, andthe transmitting device may correspond to an access point (AP). Areceiving device of the present embodiment may correspond to a station(STA) (non-AP STA) having FDD capability.

The AP transmits a trigger frame to a first STA and a second STA.

The AP transmits a first downlink (DL) PPDU to the first STA, based onthe trigger frame.

The AP transmits a second DL PPDU to the second STA, based on thetrigger frame.

The AP receives a first uplink (UL) PPDU from the second STA, based onthe trigger frame.

The trigger frame includes bandwidth information of a primary channeland secondary channel.

The first DL PPDU is transmitted through the primary channel, and thesecond DL PPDU and the first UL PPDU are transmitted through thesecondary channel.

The first and second DL PPDUs are simultaneously transmitted. The firstDL PPDU and the second DL PPDU may have the same transmission starttime, but a transmission end time may be different from each other.

The first UL PPDU is received when a pre-set duration elapses after thesecond DL PPDU is transmitted. That is, the first UL PPDU and the secondDL PPDU are identical in a frequency domain, and may be identified in atime domain.

The trigger frame, the first DL and second DL PPDUs, and the first ULPPDU may be a frame or PPDU used in the 802.11ax system, or may be newlydefined in the next-generation WLAN system.

The first DL PPDU may include a first preamble and a first data field.The second DL PPDU may include only a second preamble, or may includethe second preamble and a quality of service (QoS) null frame.

The second preamble may be a preamble obtained by duplicating the firstpreamble.

The second preamble may include a legacy-short training field (L-STF), alegacy-long training field (L-LTF), a legacy-signal (L-SIG), and anFDD-signal (FDD-SIG). The FDD-SIG may include bandwidth information ofthe primary channel and secondary channel.

The pre-set duration may be set to a first duration or a secondduration. The first duration may be a short inter-frame space (SIFS),and the second duration may be a duration having a value greater thanthe SIFS and less than a point coordination function inter-frame space(PIFS).

The first UL PPDU may include only a second data field, or may includeonly an ACK frame for the first DL PPDU, or may include a frame obtainedby aggregating the second data field and the ACK frame. The ACK framemay include a block Ack (BA) frame.

The first UL PPDU may not include an ACK frame for the second DL PPDU.In practice, the ACK frame for the second DL PPDU is not required.

A transmission end time of the first UL PPDU may be equal or prior to atransmission end time of the first DL PPDU. The L-SIG may includeinformation on the transmission end time of the first DL PPDU.

The trigger frame may further include information on a center frame, achannel number of the primary channel and secondary channel, indicationinformation of DL and UL PPDUs, duration information of the DL and ULPPDUs, and transmission opportunity (TXOP) information of the DL and ULPPDUs.

The trigger frame may include a first trigger frame transmitted in theprimary channel and a second trigger frame transmitted in the secondarychannel.

The second trigger frame may be obtained by duplicating the firsttrigger frame.

If the second trigger frame is aggregated with a physical layer servicedata unit (PSDU) included in the second DL PPDU, the first UL PPDU maybe received when an SIFS elapses after the trigger frame is transmitted.In this case, the second trigger frame may be composed of independenttrigger frames, instead of duplicating the first trigger frame.

The present specification proposes a scheme of transmitting andreceiving a physical layer protocol data unit (PPDU), based on frequencydivision duplex (FDD), in a wireless local area network (WLAN) system.

According to an embodiment proposed in the present specification, sincea PPDU is transmitted and received based on FDD by using a trigger frameor a request to send (RTS)/clear to send (CTS) frame, fast ULtransmission is possible in a scheduling manner without channelcontention. As a result, a throughput of UL transmission can beguaranteed, and a problem of low-latency communication can be solved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

FIG. 4 is a diagram illustrating a layout of resource units (RUs) usedin a band of 20 MHz.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) usedin a band of 40 MHz.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) usedin a band of 80 MHz.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B accordingto an embodiment.

FIG. 9 illustrates an example of a trigger frame.

FIG. 10 illustrates an example of a common information field.

FIG. 11 illustrates an example of a sub-field being included in a peruser information field.

FIG. 12 illustrates one example of an HE TB PPDU.

FIG. 13 is an example of applying FDD in a Wi-Fi system.

FIG. 14 shows an example in which DL or UL transmission operates with aplurality of carriers in a Wi-Fi system.

FIG. 15 shows an example of a frame structure capable of transmitting aDL PPDU through a primary channel and a UL PPDU through a secondarychannel.

FIG. 16 shows an example of a frame structure to which FDD is appliedwhen a length of a UL PPDU is longer than a length of a DL PPDU.

FIG. 17 is an example of a frame structure to which FDD is applied byusing an RTS frame and a CTS frame.

FIG. 18 is another example of a frame structure to which FDD is appliedby using an RTS frame and a CTS frame.

FIG. 19 and FIG. 20 are examples of a frame structure to which FDD isapplied by using a trigger frame.

FIG. 21 shows a procedure in which a PPDU is transmitted based on FDDaccording to the present embodiment.

FIG. 22 is a flowchart illustrating a procedure in which a PPDU istransmitted and received based on FDD from an AP perspective accordingto the present embodiment.

FIG. 23 is a flowchart illustrating a procedure in which a PPDU istransmitted and received based on FDD from an STA perspective accordingto the present embodiment.

FIG. 24 is a diagram showing a device for implementing theabove-described method.

FIG. 25 shows a more detailed wireless device implementing an exemplaryembodiment of the present disclosure.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

An upper part of FIG. 1 illustrates the structure of an infrastructurebasic service set (BSS) of institute of electrical and electronicengineers (IEEE) 802.11.

Referring the upper part of FIG. 1, the wireless LAN system may includeone or more infrastructure BSSs 100 and 105 (hereinafter, referred to asBSS). The BSSs 100 and 105 as a set of an AP and an STA such as anaccess point (AP) 125 and a station (STA1) 100-1 which are successfullysynchronized to communicate with each other are not concepts indicatinga specific region. The BSS 105 may include one or more STAs 105-1 and105-2 which may be joined to one AP 130.

The BSS may include at least one STA, APs providing a distributionservice, and a distribution system (DS) 110 connecting multiple APs.

The distribution system 110 may implement an extended service set (ESS)140 extended by connecting the multiple BSSs 100 and 105. The ESS 140may be used as a term indicating one network configured by connectingone or more APs 125 or 230 through the distribution system 110. The APincluded in one ESS 140 may have the same service set identification(SSID).

A portal 120 may serve as a bridge which connects the wireless LANnetwork (IEEE 802.11) and another network (e.g., 802. X).

In the BSS illustrated in the upper part of FIG. 1, a network betweenthe APs 125 and 130 and a network between the APs 125 and 130 and theSTAs 100-1, 105-1, and 105-2 may be implemented. However, the network isconfigured even between the STAs without the APs 125 and 130 to performcommunication. A network in which the communication is performed byconfiguring the network even between the STAs without the APs 125 and130 is defined as an Ad-Hoc network or an independent basic service set(IBSS).

A lower part of FIG. 1 illustrates a conceptual view illustrating theIBSS.

Referring to the lower part of FIG. 1, the IBSS is a BSS that operatesin an Ad-Hoc mode. Since the IBSS does not include the access point(AP), a centerized management entity that performs a management functionat the center does not exist. That is, in the IBSS, STAs 150-1, 150-2,150-3, 155-4, and 155-5 are managed by a distributed manner. In theIBSS, all STAs 150-1, 150-2, 150-3, 155-4, and 155-5 may be constitutedby movable STAs and are not permitted to access the DS to constitute aself-contained network.

The STA as a predetermined functional medium that includes a mediumaccess control (MAC) that follows a regulation of an Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard and aphysical layer interface for a radio medium may be used as a meaningincluding all of the APs and the non-AP stations (STAs).

The STA may be called various a name such as a mobile terminal, awireless device, a wireless transmit/receive unit (WTRU), user equipment(UE), a mobile station (MS), a mobile subscriber unit, or just a user.

Meanwhile, the term user may be used in diverse meanings, for example,in wireless LAN communication, this term may be used to signify a STAparticipating in uplink MU MIMO and/or uplink OFDMA transmission.However, the meaning of this term will not be limited only to this.

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

As illustrated in FIG. 2, various types of PHY protocol data units(PPDUs) may be used in a standard such as IEEE a/g/n/ac, etc. In detail,LTF and STF fields include a training signal, SIG-A and SIG-B includecontrol information for a receiving station, and a data field includesuser data corresponding to a PSDU.

In the embodiment, an improved technique is provided, which isassociated with a signal (alternatively, a control information field)used for the data field of the PPDU. The signal provided in theembodiment may be applied onto high efficiency PPDU (HE PPDU) accordingto an IEEE 802.11ax standard. That is, the signal improved in theembodiment may be HE-SIG-A and/or HE-SIG-B included in the HE PPDU. TheHE-SIG-A and the HE-SIG-B may be represented even as the SIG-A andSIG-B, respectively. However, the improved signal proposed in theembodiment is not particularly limited to an HE-SIG-A and/or HE-SIG-Bstandard and may be applied to control/data fields having various names,which include the control information in a wireless communication systemtransferring the user data.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

The control information field provided in the embodiment may be theHE-SIG-B included in the HE PPDU. The HE PPDU according to FIG. 3 is oneexample of the PPDU for multiple users and only the PPDU for themultiple users may include the HE-SIG-B and the corresponding HE SIG-Bmay be omitted in a PPDU for a single user.

As illustrated in FIG. 3, the HE-PPDU for multiple users (MUs) mayinclude a legacy-short training field (L-STF), a legacy-long trainingfield (L-LTF), a legacy-signal (L-SIG), a high efficiency-signal A(HE-SIG A), a high efficiency-signal-B (HE-SIG B), a highefficiency-short training field (HE-STF), a high efficiency-longtraining field (HE-LTF), a data field (alternatively, an MAC payload),and a packet extension (PE) field. The respective fields may betransmitted during an illustrated time period (that is, 4 or 8 μs).

More detailed description of the respective fields of FIG. 3 will bemade below.

FIG. 4 is a diagram illustrating a layout of resource units (RUs) usedin a band of 20 MHz.

As illustrated in FIG. 4, resource units (RUs) corresponding to tone(that is, subcarriers) of different numbers are used to constitute somefields of the HE-PPDU. For example, the resources may be allocated bythe unit of the RU illustrated for the HE-STF, the HE-LTF, and the datafield.

As illustrated in an uppermost part of FIG. 4, 26 units (that is, unitscorresponding to 26 tones). 6 tones may be used as a guard band in aleftmost band of the 20 MHz band and 5 tones may be used as the guardband in a rightmost band of the 20 MHz band. Further, 7 DC tones may beinserted into a center band, that is, a DC band and a 26-unitcorresponding to each 13 tones may be present at left and right sides ofthe DC band. The 26-unit, a 52-unit, and a 106-unit may be allocated toother bands. Each unit may be allocated for a receiving station, thatis, a user.

Meanwhile, the RU layout of FIG. 4 may be used even in a situation for asingle user (SU) in addition to the multiple users (MUs) and in thiscase, as illustrated in a lowermost part of FIG. 4, one 242-unit may beused and in this case, three DC tones may be inserted. [79] In oneexample of FIG. 4, RUs having various sizes, that is, a 26-RU, a 52-RU,a 106-RU, a 242-RU, and the like are proposed, and as a result, sincedetailed sizes of the RUs may extend or increase, the embodiment is notlimited to a detailed size (that is, the number of corresponding tones)of each RU.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) usedin a band of 40 MHz.

Similarly to a case in which the RUs having various RUs are used in oneexample of FIG. 4, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and the likemay be used even in one example of FIG. 5. Further, 5 DC tones may beinserted into a center frequency, 12 tones may be used as the guard bandin the leftmost band of the 40 MHz band and 11 tones may be used as theguard band in the rightmost band of the 40 MHz band.

In addition, as illustrated in FIG. 5, when the RU layout is used forthe single user, the 484-RU may be used. That is, the detailed number ofRUs may be modified similarly to one example of FIG. 4.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) usedin a band of 80 MHz.

Similarly to a case in which the RUs having various RUs are used in oneexample of each of FIG. 4 or 5, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU,and the like may be used even in one example of FIG. 6. Further, 7 DCtones may be inserted into the center frequency, 12 tones may be used asthe guard band in the leftmost band of the 80 MHz band and 11 tones maybe used as the guard band in the rightmost band of the 80 MHz band. Inaddition, the 26-RU may be used, which uses 13 tones positioned at eachof left and right sides of the DC band.

Moreover, as illustrated in FIG. 6, when the RU layout is used for thesingle user, 996-RU may be used and in this case, 5 DC tones may beinserted.

Meanwhile, the detailed number of RUs may be modified similarly to oneexample of each of FIG. 4 or 5.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

A block illustrated in FIG. 7 is another example of describing theHE-PPDU block of FIG. 3 in terms of a frequency.

An illustrated L-STF 700 may include a short training orthogonalfrequency division multiplexing (OFDM) symbol. The L-STF 700 may be usedfor frame detection, automatic gain control (AGC), diversity detection,and coarse frequency/time synchronization.

An L-LTF 710 may include a long training orthogonal frequency divisionmultiplexing (OFDM) symbol. The L-LTF 710 may be used for finefrequency/time synchronization and channel prediction.

An L-SIG 720 may be used for transmitting control information. The L-SIG720 may include information regarding a data rate and a data length.Further, the L-SIG 720 may be repeatedly transmitted. That is, a newformat, in which the L-SIG 720 is repeated (for example, may be referredto as R-LSIG) may be configured.

An HE-SIG-A 730 may include the control information common to thereceiving station.

In detail, the HE-SIG-A 730 may include information on 1) a DL/ULindicator, 2) a BSS color field indicating an identify of a BSS, 3) afield indicating a remaining time of a current TXOP period, 4) abandwidth field indicating at least one of 20, 40, 80, 160 and 80+80MHz, 5) a field indicating an MCS technique applied to the HE-SIG-B, 6)an indication field regarding whether the HE-SIG-B is modulated by adual subcarrier modulation technique for MCS, 7) a field indicating thenumber of symbols used for the HE-SIG-B, 8) a field indicating whetherthe HE-SIG-B is configured for a full bandwidth MIMO transmission, 9) afield indicating the number of symbols of the HE-LTF, 10) a fieldindicating the length of the HE-LTF and a CP length, 11) a fieldindicating whether an OFDM symbol is present for LDPC coding, 12) afield indicating control information regarding packet extension (PE),13) a field indicating information on a CRC field of the HE-SIG-A, andthe like. A detailed field of the HE-SIG-A may be added or partiallyomitted. Further, some fields of the HE-SIG-A may be partially added oromitted in other environments other than a multi-user (MU) environment.

In addition, the HE-SIG-A 730 may be composed of two parts: HE-SIG-A1and HE-SIG-A2. HE-SIG-A1 and HE-SIG-A2 included in the HE-SIG-A may bedefined by the following format structure (fields) according to thePPDU. First, the HE-SIG-A field of the HE SU PPDU may be defined asfollows.

TABLE 1 Two Parts of Number HE-SIG-A Bit Field of bits DescriptionHE-SIG-A1 B0 Format 1 Differentiate an HE SU PPDU and HE ER SU PPDU froman HE TB PPDU: Set to 1 for an HE SU PPDU and HE ER SU PPDU B1 Beam 1Set to 1 to indicate that the pre-HE modulated Change fields of the PPDUare spatially mapped differently from the first symbol of the HE-LTF.Equation (28-6), Equation (28-9), Equation (28-12), Equation (28-14),Equation (28-16) and Equation (28-18) apply if the Beam Change field isset to 1. Set to 0 to indicate that the pre-HE modulated fields of thePPDU are spatially mapped the same way as the first symbol of the HE-LTFon each tone. Equation (28-8), Equation (28-10), Equation (28-13),Equation (28-15), Equation (28-17) and Equation (28-19) apply if theBeam Change field is set to 0. (#16803) B2 UL/DL 1 Indicates whether thePPDU is sent UL or DL. Set to the value indicated by the TXVECTORparameter UPLINK_FLAG. B3-B6 MCS 4 For an HE SU PPDU: Set to n for MCSn,where n = 0, 1, 2, . . . , 11 Values 12-15 are reserved For HE ER SUPPDU with Bandwidth field set to 0 (242-tone RU): Set to n for MCSn,where n = 0, 1, 2 Values 3-15 are reserved For HE ER SU PPDU withBandwidth field set to 1 (upper frequency 106-tone RU): Set to 0 for MCS0 Values 1-15 are reserved B7 DCM 1 Indicates whether or not DCM isapplied to the Data field for the MCS indicated. If the STBC field is 0,then set to 1 to indicate that DCM is applied to the Data field. NeitherDCM nor STBC shall be applied if(#15489) both the DCM and STBC are setto 1. Set to 0 to indicate that DCM is not applied to the Data field.NOTE-DCM is applied only to HE-MCSs 0, 1, 3 and 4. DCM is applied onlyto 1 and 2 spatial streams. DCM is not applied in combination withSTBC(#15490).  B8-B13 BSS Color 6 The BSS Color field is an identifierof the BSS. Set to the value of the TXVECTOR parameter BSS_COLOR.  B14Reserved 1 Reserved and set to 1 B15-B18 Spatial 4 Indicates whether ornot spatial reuse is allowed Reuse during the transmission of thisPPDU(#16804). Set to a value from Table 28-21 (Spatial Reuse fieldencoding for an HE SU PPDU, HE ER SU PPDU, and HE MU PPDU), see 27.11.6(SPATIAL_REUSE). Set to SRP_DISALLOW to prohibit SRP-based spatial reuseduring this PPDU. Set to SRP_AND_NON_SRG_OBSS_PD_PROHIBITED to prohibitboth SRP-based spatial reuse and non-SRG OBSS PD-based spatial reuseduring this PPDU. For the interpretation of other values see 27.11.6(SPATIAL_REUSE) and 27.9 (Spatial reuse operation). B19-B20 Bandwidth 2For an HE SU PPDU: Set to 0 for 20 MHz Set to 1 for 40 MHz Set to 2 for80 MHz Set to 3 for 160 MHz and 80 + 80 MHz For an HE ER SU PPDU: Set to0 for 242-tone RU Set to 1 for upper frequency 106-tone RU within theprimary 20 MHz Values 2 and 3 are reserved B21-B22 GI + LTF Size 2Indicates the GI duration and HE-LTF size. Set to 0 to indicate a 1xHE-LTF and 0.8 μs GI Set to 1 to indicate a 2x HE-LTF and 0.8 μs GI Setto 2 to indicate a 2x HE-LTF and 1.6 μs GI Set to 3 to indicate: a 4xHE-LTF and 0.8 μs GI if both the DCM and STBC fields are 1. Neither DCMnor STBC shall be applied if(#Ed) both the DCM and STBC fields are setto 1. a 4x HE-LTF and 3.2 μs GI, otherwise B23-B25 NSTS And 3 If theDoppler field is 0, indicates the number Midamble of space-time streams.Periodicity Set to the number of space-time streams minus 1 For an HE ERSU PPDU, values 2 to 7 are reserved If the Doppler field is 1, thenB23-B24 indicates the number of space time streams, up to 4, and B25indicates the midamble periodicity. B23-B24 is set to the number ofspace time streams minus 1. For an HE ER SU PPDU, values 2 and 3 arereserved B25 is set to 0 if TXVECTOR parameter MIDAMBLE_PERIODICITY is10 and set to 1 if TXVECTOR parameter MIDAMBLE_PERIODICITY is 20.HE-SIG-A2 B0-B6 TXOP 7 Set to 127 to indicate no duration information(HE SU if(#15491) TXVECTOR parameter TXOP_DURATION PPDU)or is set toUNSPECIFIED. HE-SIG-A3 Set to a value less than 127 to indicate duration(HE ER information for NAV setting and protection of the SU PPDU) TXOPas follows: If TXVECTOR parameter TXOP_DURAT1ON is less than 512, thenB0 is set to 0 and B1-B6 is set to floor(TXOP_DURATION/8)(#16277).Otherwise, B0 is set to 1 and B1-B6 is set to floor((TXOP_DURATION-512)/128)(#16277). where(#16061) B0 indicates the TXOPlength granularity. Set to 0 for 8 μs; otherwise set to 1 for 128 μs.B1-B6 indicates the scaled value of the TXOP_DURATION B7 Coding 1Indicates whether BCC or LDPC is used: Set to 0 to indicate BCC Set to 1to indicate LDPC B8 LDPC Extra 1 Indicates the presence of the extraOFDM Symbol symbol segment for LDPC: Segment Set to 1 if an extra OFDMsymbol segment for LDPC is present Set to 0 if an extra OFDM symbolsegment for LDPC is not present Reserved and set to 1 if the Codingfield is set to 0(#15492). B9 STBC 1 If the DCM field is set to 0, thenset to 1 if space time block coding is used. Neither DCM nor STBC shallbe applied if(#15493) both the DCM field and STBC field are set to 1.Set to 0 otherwise.  B10 Beam- 1 Set to 1 if a beamforming steeringmatrix is formed(#16038) applied to the waveform in an SU transmission.Set to 0 otherwise. B11-B12 Pre-FEC 2 Indicates the pre-FEC paddingfactor. Padding Set to 0 to indicate a pre-FEC padding factor of 4Factor Set to 1 to indicate a pre-FEC padding factor of 1 Set to 2 toindicate a pre-FEC padding factor of 2 Set to 3 to indicate a pre-FECpadding factor of 3  B13 PE 1 Indicates PE disambiguity(#16274) asdefined in Disambiguity 28.3.12 (Packet extension).  B14 Reserved 1Reserved and set to 1  B15 Doppler 1 Set to 1 if one of the followingapplies: The number of OFDM symbols in the Data field is larger than thesignaled midamble periodicity plus 1 and the midamble is present Thenumber of OFDM symbols in the Data field is less than or equal to thesignaled midamble periodicity plus 1 (see 28.3.11.16 Midamble), themidamble is not present, but the channel is fast varying. It recommendsthat midamble may be used for the PPDUs of the reverse link. Set to 0otherwise. B16-B19 CRC 4 CRC for bits 0-41 of the HE-SIG-A field (see28.3.10.7.3 (CRC computation)). Bits 0-41 of the HE-SIG-A fieldcorrespond to bits 0-25 of HE-SIG-A1 followed by bits 0-15 ofHE-SIG-A2). B20-B25 Tail 6 Used to terminate the trellis of theconvolutional decoder. Set to 0.

In addition, the HE-SIG-A field of the HE MU PPDU may be defined asfollows.

TABLE 2 Two Parts of Number HE-SIG-A Bit Field of bits DescriptionHE-SIG-A1 B0  UL/DL 1 Indicates whether the PPDU is sent UL or DL. Setto the value indicated by the TXVECTOR parameter UPLINK_FLAG. (#16805)NOTE-The TDLS peer can identify the TDLS frame by To DS and From DSfields in the MAC header of the MPDU. B1-B3 SIGB 3 Indicates the MCS ofthe HE-SIG-B field: MCS Set to 0 for MCS 0 Set to 1 for MCS 1 Set to 2for MCS 2 Set to 3 for MCS 3 Set to 4 for MCS 4 Set to 5 for MCS 5 Thevalues 6 and 7 are reserved B4  SIGB 1 Set to 1 indicates that theHE-SIG-B is DCM modulated with DCM for the MCS. Set to 0 indicates thatthe HE-SIG-B is not modulated with DCM for the MCS. NOTE-DCM is onlyapplicable to MCS 0, MCS 1, MCS 3, and MCS 4.  B5-B10 BSS 6 The BSSColor field is an identifier of the BSS. Color Set to the value of theTXVECTOR parameter BSS_COLOR. B11-B14 Spatial 4 Indicates whether or notspatial reuse is allowed Reuse during the transmission of thisPPDU(#16806). Set to the value of the SPATIAL_REUSE parameter of theTXVECTOR, which contains a value from Table 28-21 (Spatial Reuse fieldencoding for an HE SU PPDU, HE ER SU PPDU, and HE MU PPDU) (see 27.11.6(SPATIAL_REUSE)). Set to SRP_DISALLOW to prohibit SRP-based spatialreuse during this PPDU. Set to SRP_AND_NON_SRG_OBSS_PD_PROHIBITED toprohibit both SRP-based spatial reuse and non-SRG OBSS PD-based spatialreuse during this PPDU. For the interpretation of other values see27.11.6 (SPATIAL_REUSE) and 27.9 (Spatial reuse operation). B15-B17Bandwidth 3 Set to 0 for 20 MHz. Set to 1 for 40 MHz. Set to 2 for 80MHz non-preamble puncturing mode. Set to 3 for 160 MHz and 80 + 80 MHznon-preamble puncturing mode. If the SIGB Compression field is 0: Set to4 for preamble puncturing in 80 MHz, where in the preamble only thesecondary 20 MHz is punctured. Set to 5 for preamble puncturing in 80MHz, where in the preamble only one of the two 20 MHz subchannels insecondary 40 MHz is punctured. Set to 6 for preamble puncturing in 160MHz or 80 + 80 MHz, where in the primary 80 MHz of the preamble only thesecondary 20 MHz is punctured. Set to 7 for preamble puncturing in 160MHz or 80 + 80 MHz, where in the primary 80 MHz of the preamble theprimary 40 MHz is present. If the SIGB Compression field is 1 thenvalues 4-7 are reserved. B18-B21 Number Of 4 If the HE-SIG-B Compressionfield is set to 0, HE-SIG-B indicates the number of OFDM symbols in theSymbols Or HE-SIG-B field: (#15494) MU-MIMO Set to the number of OFDMsymbols in the Users HE-SIG-B field minus 1 if the number of OFDMsymbols in the HE-SIG-B field is less than 16; Set to 15 to indicatethat the number of OFDM symbols in the HE-SIG-B field is equal to 16 ifLonger Than 16 HE SIG-B OFDM Symbols Support sub-field of the HECapabilities element transmitted by at least one recipient STA is 0; Setto 15 to indicate that the number of OFDM symbols in the HE-SIG-B fieldis greater than or equal to 16 if the Longer than 16 HE SIG-B OFDMSymbols Support subfield of the HE Capabilities element transmitted byall the recipient STAs are 1 and if the HE-SIG-B data rate is less thanMCS 4 without DCM. The exact number of OFDM symbols in the HE-SIG-Bfield is calculated based on the number of User fields in the HE-SIG-Bcontent channel which is indicated by HE-SIG-B common field in thiscase. If the HE-SIG-B Compression field is set to 1, indicates thenumber of MU-MIMO users and is set to the number of NU-MIMO users minus1(#15495). B22 SIGB 1 Set to 0 if the Common field in HE-SIG-B ispresent. Compression Set to 1 if the Common field in HE-SIG-B is notpresent. (#16139) B23-B24 GI + LTF Size 2 Indicates the GI duration andHE-LTF size: Set to 0 to indicate a 4x HE-LTF and 0.8 μs GI Set to 1 toindicate a 2x HE-LTF and 0.8 μs GI Set to 2 to indicate a 2x HE-LTF and1.6 μs GI Set to 3 to indicate a 4x HE-LTF and 3.2 μs GI B25 Doppler 1Set to 1 if one of the following applies: The number of OFDM symbols inthe Data field is larger than the signaled midamble periodicity plus 1and the midamble is present The number of OFDM symbols in the Data fieldis less than or equal to the signaled midamble periodicity plus 1 (see28.3.11.16 Midamble), the midamble is not present, but the channel isfast varying. It recommends that midamble may be used for the PPDUs ofthe reverse link. Set to 0 otherwise. HE-SIG-A2 B0-B6 TXOP 7 Set to 127to indicate no duration information if(#15496) TXVECTOR parameterTXOP_DURATION is set to UNSPECIFIED. Set to a value less than 127 toindicate duration information for NAV setting and protection of the TXOPas follows: If TXVECTOR parameter TXOP_DURATION is less than 512, thenB0 is set to 0 and B1-B6 is set to floor(TXOP_DURATION/8)(#16277).Otherwise, B0 is set to 1 and B1-B6 is set to floor((TXOP_DURATION-512)/128)(#16277). where(#16061) B0 indicates the TXOPlength granularity. Set to 0 for 8 μs; otherwise set to 1 for 128 μs.B1-B6 indicates the scaled value of the TXOP_DURATION B7  Reserved 1Reserved and set to 1  B8-B10 Number of 3 If the Doppler field is set to0(#15497), HE-LTF indicates the number of HE-LTF symbols: Symbols AndSet to 0 for 1 HE-LTF symbol Midamble Set to 1 for 2 HE-LTF symbolsPeriodicity Set to 2 for 4 HE-LTF symbols Set to 3 for 6 HE-LTF symbolsSet to 4 for 8 HE-LTF symbols Other values are reserved. If the Dopplerfield is set to 1(#15498), B8-B9 indicates the number of HE-LTFsymbols(#16056) and B10 indicates midamble periodicity: B8-B9 is encodedas follows: 0 indicates 1 HE-LTF symbol 1 indicates 2 HE-LTF symbols 2indicates 4 HE-LTF symbols 3 is reserved B10 is set to 0 if the TXVECTORparameter MIDAMBLE_PERIODICITY is 10 and set to 1 if the TXVECTORparameter PREAMBLE_PERIODICITY is 20. B11 LDPC Extra 1 Indication of thepresence of the extra OFDM symbol Symbol segment for LDPC. Segment Setto 1 if an extra OFDM symbol segment for LDPC is present. Set to 0otherwise. B12 STBC 1 In an HE MU PPDU where each RU includes no morethan 1 user, set to 1 to indicate all RUs are STBC encoded in thepayload, set to 0 to indicate all RUs are not STBC encoded in thepayload. STBC does not apply to HE-SIG-B. STBC is not applied if one ormore RUs are used for MU-MIMO allocation. (#15661) B13-B14 Pre-FEC 2Indicates the pre-FEC padding factor. Padding Set to 0 to indicate apre-FEC padding factor of 4 Factor Set to 1 to indicate a pre-FECpadding factor of 1 Set to 2 to indicate a pre-FEC padding factor of 2Set to 3 to indicate a pre-FEC padding factor of 3 B15 PE 1 Indicates PEdisambiguity(#16274) as defined in Disambiguity 28.3.12 (Packetextension). B16-B19 CRC 4 CRC for bits 0-41 of the HE-SIG-A field (see28.3.10.7.3 (CRC computation)). Bits 0-41 of the HE-SIG-A fieldcorrespond to bits 0-25 of HE-SIG-A1 followed by bits 0-15 ofHE-SIG-A2). B20-B25 Tail 6 Used to terminate the trellis of theconvolutional decoder. Set to 0.

In addition, the HE-SIG-A field of the HE TB PPDU may be defined asfollows.

TABLE 3 Two Parts of Number HE-SIG-A Bit Field of bits DescriptionHE-SIG-A1 B0  Format 1 Differentiate an HE SU PPDU and HE ER SU PPDUfrom an HE TB PPDU: Set to 0 for an HE TB PPDU B1-B6 BSS 6 The BSS Colorfield is an identifier of the BSS. Color Set to the value of theTXVECTOR parameter BSS_COLOR.  B7-B10 Spatial 4 Indicates whether or notspatial reuse is allowed Reuse 1 in a subband of the PPDU during thetransmission of this PPDU, and if allowed, indicates a value that isused to determine a limit on the transmit power of a spatial reusetransmission. If the Bandwidth field indicates 20 MHz, 40 MHz, or 80 MHzthen this Spatial Reuse field applies to the first 20 MHz subband. Ifthe Bandwidth field indicates 160/80 + 80 MHz then this Spatial Reusefield applies to the first 40 MHz sub-band of the 160 MHz operatingband. Set to the value of the SPATIAL_REUSE(1) parameter of theTXVECTOR, which contains a value from Table 28-22 (Spatial Reuse fieldencoding for an HE TB PPDU) for an HE TB PPDU (see 27.11.6(SPATIAL_REUSE)). Set to SRP_DISALLOW to prohibit SRP-based spatialreuse during this PPDU. Set to SRP_AND_NON_SRG_OBSS_PD_PROHIBITED toprohibit both SRP-based spatial reuse and non-SRG OBSS PD-based spatialreuse during this PPDU. For the interpretation of other values see27.11.6 (SPATIAL_REUSE) and 27.9 (Spatial reuse operation). B11-B14Spatial 4 Indicates whether or not spatial reuse is allowed Reuse 2 in asubband of the PPDU during the transmission of this PPDU, and ifallowed, indicates a value that is used to determine a limit on thetransmit power of a spatial reuse transmission. If the Bandwidth fieldindicates 20 MHz, 40 MHz, or 80 MHz: This Spatial Reuse field applies tothe second 20 MHz subband. If(#Ed) the STA operating channel width is 20MHz, then this field is set to the same value as Spatial Reuse 1 field.If(#Ed) the STA operating channel width is 40 MHz in the 2.4 GHz band,this field is set to the same value as Spatial Reuse 1 field. If theBandwidth field indicates 160/80 + 80 MHz the this Spatial Reuse fieldapplies to the second 40 MHz subband of the 160 MHz operating band. Setto the value of the SPATIAL_REUSE(2) parameter of the TXVECTOR, whichcontains a value from Table 28-22 (Spatial Reuse field encoding for anHE TB PPDU) for an HE TB PPDU (see 27.11.6 (SPATIAL_REUSE)). Set toSRP_DISALLOW to prohibit SRP-based spatial reuse during this PPDU. Setto SRP_AND_NON_SRG_OBSS_PD_PROIHBITED to prohibit both SRP-based spatialreuse and non-SRG OBSS PD-based spatial reuse during this PPDU. For theinterpretation of other values see 27.11.6 (SPATIAL_REUSE) and 27.9(Spatial reuse operation). B15-B18 Spatial 4 Indicates whether or notspatial reuse is allowed Reuse 3 in a subband of the PPDU during thetransmission of this PPDU, and if allowed, indicates a value that isused to determine a limit on the transmit power of a spatial reusetransmission. If the Bandwidth field indicates 20 MHz, 40 MHz or 80 MHz:This Spatial Reuse field applies to the third 20 MHz subband. If(#Ed)the STA operating channel width is 20 MHz or 40 MHz, this field is setto the same value as Spatial Reuse 1 field. If the Bandwidth fieldindicates 160/80 + 80 MHz: This Spatial Reuse field applies to the third40 MHz subband of the 160 MHz operating band. If(#Ed) the STA operatingchannel width is 80 + 80 MHz, this field is set to the same value asSpatial Reuse 1 field. Set to the value of the SPATIAL_REUSE(3)parameter of the TXVECTOR, which contains a value from Table 28-22(Spatial Reuse field encoding for an HE TB PPDU) for an HE TB PPDU (see27.11.6 (SPATIAL_REUSE)). Set to SRP_DISALLOW to prohibit SRP-basedspatial reuse during this PPDU. Set toSRP_AND_NON_SRG_OBSS_PD_PROHIBITED to prohibit both SRP-based spatialreuse and non-SRG OBSS PD-based spatial reuse during this PPDU. For theinterpretation of other values see 27.11.6 (SPATIAL_REUSE) and 27.9(Spatial reuse operation). B19-B22 Spatial 4 Indicates whether or notspatial reuse is allowed Reuse 4 in a subband of the PPDU during thetransmission of this PPDU, and if allowed, indicates a value that isused to determine a limit on the transmit power of a spatial reusetransmission. If the Bandwidth field indicates 20 MHz, 40 MHz or 80 MHz:This Spatial Reuse field applies to the fourth 20 MHz subband. If(#Ed)the STA operating channel width is 20 MHz, then this field is set to thesame value as Spatial Reuse 1 field. If(#Ed) the STA operating channelwidth is 40 MHz, then this field is set to the same value as SpatialReuse 2 field. If the Bandwidth field indicates 160/80 + 80 MHz: ThisSpatial Reuse field applies to the fourth 40 MHz subband of the 160 MHzoperating band. If(#Ed) the STA operating channel width is 80 + 80 MHz,then this field is set to same value as Spatial Reuse 2 field. Set tothe value of the SPATIAL_REUSE(4) parameter of the TXVECTOR, whichcontains a value from Table 28-22 (Spatial Reuse field encoding for anHE TB PPDU) for an HE TB PPDU (see 27.11.6 (SPATIAL_REUSE)). Set toSRP_DISALLOW to prohibit SRP-based spatial reuse during this PPDU. Setto SRP_AND_NON_SRG_OBSS_PD_PROHIBITED to prohibit both SRP-based spatialreuse and non-SRG OBSS PD-based spatial reuse during this PPDU. For theinterpretation of other values see 27.11.6 (SPATIAL_REUSE) and 27.9(Spatial reuse operation). B23 Reserved 1 Reserved and set to 1.NOTE-Unlike other Reserved fields in HE-SIG-A of the HE TB PPDU, B23does not have a corresponding bit in the Trigger frame. B24-B25Bandwidth 2 (#16003)Set to 0 for 20 MHz Set to 1 for 40 MHz Set to 2 for80 MHz Set to 3 for 160 MHz and 80 + 80 MHz HE-STG-A2 B0-B6 TXOP 7 Setto 127 to indicate no duration information if(#15499) TXVECTOR parameterTXOP_DURATION is set to UNSPECIFIED. Set to a value less than 127 toindicate duration information for NAV setting and protection of the TXOPas follows: If TXVECTOR parameter TXOP_DURATION is less than 512, thenB0 is set to 0 and B1-B6 is set to floor(TXOP_DURATION/8)(#16277).Otherwise, B0 is set to 1 and B1-B6 is set to floor ((TXOP_DURATION -512)/128)(#16277). where(#16061) B0 indicates the TXOP lengthgranularity. Set to 0 for 8 μs: otherwise set to 1 for 128 μs. B1-B6indicates the scaled value of the TXOP_DURATION  B7-B15 Reserved 9Reserved and set to value indicated in the UL HE-SIG-A2 Reservedsubfield in the Trigger frame. B16-B19 CRC 4 CRC of bits 0-41 of theHE-SIG-A field. See 28.3.10.7.3 (CRC computation). Bits 0-41 of theHE-SIG-A field correspond to bits 0-25 of HE-SIG-A1 followed by bits0-15 of HE-SIG-A2). B20-B25 Tail 6 Used to terminate the trellis of theconvolutional decoder. Set to 0.

An HE-SIG-B 740 may be included only in the case of the PPDU for themultiple users (MUs) as described above. Principally, an HE-SIG-A 750 oran HE-SIG-B 760 may include resource allocation information(alternatively, virtual resource allocation information) for at leastone receiving STA.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B accordingto an embodiment.

As illustrated in FIG. 8, the HE-SIG-B field includes a common field ata frontmost part and the corresponding common field is separated from afield which follows therebehind to be encoded. That is, as illustratedin FIG. 8, the HE-SIG-B field may include a common field including thecommon control information and a user-specific field includinguser-specific control information. In this case, the common field mayinclude a CRC field corresponding to the common field, and the like andmay be coded to be one BCC block. The user-specific field subsequentthereafter may be coded to be one BCC block including the “user-specificfield” for 2 users and a CRC field corresponding thereto as illustratedin FIG. 8.

A previous field of the HE-SIG-B 740 may be transmitted in a duplicatedform on an MU PPDU. In the case of the HE-SIG-B 740, the HE-SIG-B 740transmitted in some frequency band (e.g., a fourth frequency band) mayeven include control information for a data field corresponding to acorresponding frequency band (that is, the fourth frequency band) and adata field of another frequency band (e.g., a second frequency band)other than the corresponding frequency band. Further, a format may beprovided, in which the HE-SIG-B 740 in a specific frequency band (e.g.,the second frequency band) is duplicated with the HE-SIG-B 740 ofanother frequency band (e.g., the fourth frequency band). Alternatively,the HE-SIG B 740 may be transmitted in an encoded form on alltransmission resources. A field after the HE-SIG B 740 may includeindividual information for respective receiving STAs receiving the PPDU.

The HE-STF 750 may be used for improving automatic gain controlestimation in a multiple input multiple output (MIMO) environment or anOFDMA environment.

The HE-LTF 760 may be used for estimating a channel in the MIMOenvironment or the OFDMA environment.

The size of fast Fourier transform (FFT)/inverse fast Fourier transform(IFFT) applied to the HE-STF 750 and the field after the HE-STF 750, andthe size of the FFT/IFFT applied to the field before the HE-STF 750 maybe different from each other. For example, the size of the FFT/IFFTapplied to the HE-STF 750 and the field after the HE-STF 750 may be fourtimes larger than the size of the FFT/IFFT applied to the field beforethe HE-STF 750.

For example, when at least one field of the L-STF 700, the L-LTF 710,the L-SIG 720, the HE-SIG-A 730, and the HE-SIG-B 740 on the PPDU ofFIG. 7 is referred to as a first field, at least one of the data field770, the HE-STF 750, and the HE-LTF 760 may be referred to as a secondfield. The first field may include a field associated with a legacysystem and the second field may include a field associated with an HEsystem. In this case, the fast Fourier transform (FFT) size and theinverse fast Fourier transform (IFFT) size may be defined as a sizewhich is N (N is a natural number, e.g., N=1, 2, and 4) times largerthan the FFT/IFFT size used in the legacy wireless LAN system. That is,the FFT/IFFT having the size may be applied, which is N (=4) timeslarger than the first field of the HE PPDU. For example, 256 FFT/IFFTmay be applied to a bandwidth of 20 MHz, 512 FFT/IFFT may be applied toa bandwidth of 40 MHz, 1024 FFT/IFFT may be applied to a bandwidth of 80MHz, and 2048 FFT/IFFT may be applied to a bandwidth of continuous 160MHz or discontinuous 160 MHz.

In other words, a subcarrier space/subcarrier spacing may have a sizewhich is 1/N times (N is the natural number, e.g., N=4, the subcarrierspacing is set to 78.125 kHz) the subcarrier space used in the legacywireless LAN system. That is, subcarrier spacing having a size of 312.5kHz, which is legacy subcarrier spacing may be applied to the firstfield of the HE PPDU and a subcarrier space having a size of 78.125 kHzmay be applied to the second field of the HE PPDU.

Alternatively, an IDFT/DFT period applied to each symbol of the firstfield may be expressed to be N (=4) times shorter than the IDFT/DFTperiod applied to each data symbol of the second field. That is, theIDFT/DFT length applied to each symbol of the first field of the HE PPDUmay be expressed as 3.2 μs and the IDFT/DFT length applied to eachsymbol of the second field of the HE PPDU may be expressed as 3.2 μs * 4(=12.8 μs). The length of the OFDM symbol may be a value acquired byadding the length of a guard interval (GI) to the IDFT/DFT length. Thelength of the GI may have various values such as 0.4 μs, 0.8 μs, 1.6 μs,2.4 μs, and 3.2 μs.

For simplicity in the description, in FIG. 7, it is expressed that afrequency band used by the first field and a frequency band used by thesecond field accurately coincide with each other, but both frequencybands may not completely coincide with each other, in actual. Forexample, a primary band of the first field (L-STF, L-LTF, L-SIG,HE-SIG-A, and HE-SIG-B) corresponding to the first frequency band may bethe same as the most portions of a frequency band of the second field(HE-STF, HE-LTF, and Data), but boundary surfaces of the respectivefrequency bands may not coincide with each other. As illustrated inFIGS. 4 to 6, since multiple null subcarriers, DC tones, guard tones,and the like are inserted during arranging the RUs, it may be difficultto accurately adjust the boundary surfaces.

The user (e.g., a receiving station) may receive the HE-SIG-A 730 andmay be instructed to receive the downlink PPDU based on the HE-SIG-A730. In this case, the STA may perform decoding based on the FFT sizechanged from the HE-STF 750 and the field after the HE-STF 750. On thecontrary, when the STA may not be instructed to receive the downlinkPPDU based on the HE-SIG-A 730, the STA may stop the decoding andconfigure a network allocation vector (NAV). A cyclic prefix (CP) of theHE-STF 750 may have a larger size than the CP of another field and theduring the CP period, the STA may perform the decoding for the downlinkPPDU by changing the FFT size.

Hereinafter, in the embodiment of the present disclosure, data(alternatively, or a frame) which the AP transmits to the STA may beexpressed as a terms called downlink data (alternatively, a downlinkframe) and data (alternatively, a frame) which the STA transmits to theAP may be expressed as a term called uplink data (alternatively, anuplink frame). Further, transmission from the AP to the STA may beexpressed as downlink transmission and transmission from the STA to theAP may be expressed as a term called uplink transmission.

In addition, a PHY protocol data unit (PPDU), a frame, and datatransmitted through the downlink transmission may be expressed as termssuch as a downlink PPDU, a downlink frame, and downlink data,respectively. The PPDU may be a data unit including a PPDU header and aphysical layer service data unit (PSDU) (alternatively, a MAC protocoldata unit (MPDU)). The PPDU header may include a PHY header and a PHYpreamble and the PSDU (alternatively, MPDU) may include the frame orindicate the frame (alternatively, an information unit of the MAC layer)or be a data unit indicating the frame. The PHY header may be expressedas a physical layer convergence protocol (PLCP) header as another termand the PHY preamble may be expressed as a PLCP preamble as anotherterm.

Further, a PPDU, a frame, and data transmitted through the uplinktransmission may be expressed as terms such as an uplink PPDU, an uplinkframe, and uplink data, respectively.

In the wireless LAN system to which the embodiment of the presentdescription is applied, the total bandwidth may be used for downlinktransmission to one STA and uplink transmission to one STA. Further, inthe wireless LAN system to which the embodiment of the presentdescription is applied, the AP may perform downlink (DL) multi-user (MU)transmission based on multiple input multiple output (MU MIMO) and thetransmission may be expressed as a term called DL MU MIMO transmission.

In addition, in the wireless LAN system according to the embodiment, anorthogonal frequency division multiple access (OFDMA) based transmissionmethod is preferably supported for the uplink transmission and/ordownlink transmission. That is, data units (e.g., RUs) corresponding todifferent frequency resources are allocated to the user to performuplink/downlink communication. In detail, in the wireless LAN systemaccording to the embodiment, the AP may perform the DL MU transmissionbased on the OFDMA and the transmission may be expressed as a termcalled DL MU OFDMA transmission. When the DL MU OFDMA transmission isperformed, the AP may transmit the downlink data (alternatively, thedownlink frame and the downlink PPDU) to the plurality of respectiveSTAs through the plurality of respective frequency resources on anoverlapped time resource. The plurality of frequency resources may be aplurality of subbands (alternatively, sub channels) or a plurality ofresource units (RUs). The DL MU OFDMA transmission may be used togetherwith the DL MU MIMO transmission. For example, the DL MU MIMOtransmission based on a plurality of space-time streams (alternatively,spatial streams) may be performed on a specific subband (alternatively,sub channel) allocated for the DL MU OFDMA transmission.

Further, in the wireless LAN system according to the embodiment, uplinkmulti-user (UL MU) transmission in which the plurality of STAs transmitsdata to the AP on the same time resource may be supported. Uplinktransmission on the overlapped time resource by the plurality ofrespective STAs may be performed on a frequency domain or a spatialdomain.

When the uplink transmission by the plurality of respective STAs isperformed on the frequency domain, different frequency resources may beallocated to the plurality of respective STAs as uplink transmissionresources based on the OFDMA. The different frequency resources may bedifferent subbands (alternatively, sub channels) or different resourcesunits (RUs). The plurality of respective STAs may transmit uplink datato the AP through different frequency resources. The transmission methodthrough the different frequency resources may be expressed as a termcalled a UL MU OFDMA transmission method.

When the uplink transmission by the plurality of respective STAs isperformed on the spatial domain, different time-space streams(alternatively, spatial streams) may be allocated to the plurality ofrespective STAs and the plurality of respective STAs may transmit theuplink data to the AP through the different time-space streams. Thetransmission method through the different spatial streams may beexpressed as a term called a UL MU MIMO transmission method.

The UL MU OFDMA transmission and the UL MU MIMO transmission may be usedtogether with each other. For example, the UL MU MIMO transmission basedon the plurality of space-time streams (alternatively, spatial streams)may be performed on a specific subband (alternatively, sub channel)allocated for the UL MU OFDMA transmission.

In the legacy wireless LAN system which does not support the MU OFDMAtransmission, a multi-channel allocation method is used for allocating awider bandwidth (e.g., a 20 MHz excess bandwidth) to one terminal. Whena channel unit is 20 MHz, multiple channels may include a plurality of20 MHz-channels. In the multi-channel allocation method, a primarychannel rule is used to allocate the wider bandwidth to the terminal.When the primary channel rule is used, there is a limit for allocatingthe wider bandwidth to the terminal. In detail, according to the primarychannel rule, when a secondary channel adjacent to a primary channel isused in an overlapped BSS (OBSS) and is thus busy, the STA may useremaining channels other than the primary channel. Therefore, since theSTA may transmit the frame only to the primary channel, the STA receivesa limit for transmission of the frame through the multiple channels.That is, in the legacy wireless LAN system, the primary channel ruleused for allocating the multiple channels may be a large limit inobtaining a high throughput by operating the wider bandwidth in acurrent wireless LAN environment in which the OBSS is not small.

In order to solve the problem, in the embodiment, a wireless LAN systemis disclosed, which supports the OFDMA technology. That is, the OFDMAtechnique may be applied to at least one of downlink and uplink.Further, the MU-MIMO technique may be additionally applied to at leastone of downlink and uplink. When the OFDMA technique is used, themultiple channels may be simultaneously used by not one terminal butmultiple terminals without the limit by the primary channel rule.Therefore, the wider bandwidth may be operated to improve efficiency ofoperating a wireless resource.

As described above, in case the uplink transmission performed by each ofthe multiple STAs (e.g., non-AP STAs) is performed within the frequencydomain, the AP may allocate different frequency resources respective toeach of the multiple STAs as uplink transmission resources based onOFDMA. Additionally, as described above, the frequency resources eachbeing different from one another may correspond to different subbands(or sub-channels) or different resource units (RUs).

The different frequency resources respective to each of the multipleSTAs are indicated through a trigger frame.

FIG. 9 illustrates an example of a trigger frame. The trigger frame ofFIG. 9 allocates resources for Uplink Multiple-User (MU) transmissionand may be transmitted from the AP. The trigger frame may be configuredas a MAC frame and may be included in the PPDU. For example, the triggerframe may be transmitted through the PPDU shown in FIG. 3, through thelegacy PPDU shown in FIG. 2, or through a certain PPDU, which is newlydesigned for the corresponding trigger frame. In case the trigger frameis transmitted through the PPDU of FIG. 3, the trigger frame may beincluded in the data field shown in the drawing.

Each of the fields shown in FIG. 9 may be partially omitted, or otherfields may be added. Moreover, the length of each field may be varieddifferently as shown in the drawing.

A Frame Control field 910 shown in FIG. 9 may include informationrelated to a version of the MAC protocol and other additional controlinformation, and a Duration field 920 may include time information forconfiguring a NAV or information related to an identifier (e.g., AID) ofthe user equipment.

Also, the RA field 930 includes address information of a receiving STAof the corresponding trigger frame and may be omitted if necessary. TheTA field 940 includes address information of an STA triggering thecorresponding trigger frame (for example, an AP), and the commoninformation field 950 includes common control information applied to areceiving STA that receives the corresponding trigger frame. Forexample, a field indicating the length of the L-SIG field of the UL PPDUtransmitted in response to the corresponding trigger frame orinformation controlling the content of the SIG-A field (namely, theHE-SIG-A field) of the UL PPDU transmitted in response to thecorresponding trigger frame may be included. Also, as common controlinformation, information on the length of the CP of the UP PPDUtransmitted in response to the corresponding trigger frame orinformation on the length of the LTF field may be included.

Also, it is preferable to include a per user information field (960 #1to 960#N) corresponding to the number of receiving STAs that receive thetrigger frame of FIG. 9. The per user information field may be referredto as an “RU allocation field”.

Also, the trigger frame of FIG. 9 may include a padding field 970 and aframe check sequence field 980.

It is preferable that each of the per user information fields (960#1 to960#N) shown in FIG. 9 includes a plurality of subfields.

FIG. 10 illustrates an example of a common information field. Among thesub-fields of FIG. 10, some may be omitted, and other additionalsub-fields may also be added. Additionally, the length of each of thesub-fields shown in the drawing may be varied.

The trigger type field 1010 of FIG. 10 may indicate a trigger framevariant and encoding of the trigger frame variant. The trigger typefield 1010 may be defined as follows.

TABLE 4 Trigger Type subfield value Trigger frame variant 0 Basic 1Beamforming Report Poll (BFRP) 2 MU-BAR 3 MU-RTS 4 Buffer Status ReportPoll (BSRP) 5 GCR MU-BAR 6 Bandwidth Query Report Poll (BQRP) 7 NDPFeedback Report Poll (NFRP) 8-15 Reserved

The UL BW field 1020 of FIG. 10 indicates bandwidth in the HE-SIG-Afield of an HE Trigger Based (TB) PPDU. The UL BW field 1020 may bedefined as follows.

TABLE 5 UL BW subfield value Description 0 20 MHz 1 40 MHz 2 80 MHz 380 + 80 MHz or 160 MHz

The Guard Interval (GI) and LTF type fields 1030 of FIG. 10 indicate theGI and HE-LTF type of the HE TB PPDU response. The GI and LTF type field1030 may be defined as follows.

TABLE 6 GI And LTF field value Description 0 1x HE-LTF + 1.6 μs GI 1 2xHE-LTF + 1.6 μs GI 2 4x HE-LTF + 3.2 μs GI(#15968) 3 Reserved

Also, when the GI and LTF type fields 1030 have a value of 2 or 3, theMU-MIMO LTF mode field 1040 of FIG. 10 indicates the LTF mode of a ULMU-MIMO HE TB PPDU response. At this time, the MU-MIMO LTF mode field1040 may be defined as follows.

If the trigger frame allocates an RU that occupies the whole HE TB PPDUbandwidth and the RU is allocated to one or more STAs, the MU-MIMO LTFmode field 1040 indicates one of an HE single stream pilot HE-LTF modeor an HE masked HE-LTF sequence mode.

If the trigger frame does not allocate an RU that occupies the whole HETB PPDU bandwidth and the RU is not allocated to one or more STAs, theMU-MIMO LTF mode field 1040 indicates the HE single stream pilot HE-LTFmode. The MU-MIMO LTF mode field 1040 may be defined as follows.

TABLE 7 MU-MIMO LTF subfield value Description 0 HE single stream pilotHE-LTF mode 1 HE masked HE-LTF sequence mode

FIG. 11 illustrates an example of a sub-field being included in a peruser information field. Among the sub-fields of FIG. 11, some may beomitted, and other additional sub-fields may also be added.Additionally, the length of each of the sub-fields shown in the drawingmay be varied.

The User Identifier field of FIG. 11 (or AID12 field, 1110) indicatesthe identifier of an STA (namely, a receiving STA) corresponding to peruser information, where an example of the identifier may be the whole orpart of the AID.

Also, an RU Allocation field 1120 may be included. In other words, whena receiving STA identified by the User Identifier field 1110 transmits aUL PPDU in response to the trigger frame of FIG. 9, the corresponding ULPPDU is transmitted through an RU indicated by the RU Allocation field1120. In this case, it is preferable that the RU indicated by the RUAllocation field 1120 corresponds to the RUs shown in FIGS. 4, 5, and 6.A specific structure of the RU Allocation field 1120 will be describedlater.

The subfield of FIG. 11 may include a (UL FEC) coding type field 1130.The coding type field 1130 may indicate the coding type of an uplinkPPDU transmitted in response to the trigger frame of FIG. 9. Forexample, when BCC coding is applied to the uplink PPDU, the coding typefield 1130 may be set to ‘1’, and when LDPC coding is applied, thecoding type field 1130 may be set to ‘0’.

Additionally, the sub-field of FIG. 11 may include a UL MCS field 1140.The MCS field 1140 may indicate a MCS scheme being applied to the uplinkPPDU that is transmitted in response to the trigger frame of FIG. 9.

Also, the subfield of FIG. 11 may include a Trigger Dependent User Infofield 1150. When the Trigger Type field 1010 of FIG. 10 indicates abasic trigger variant, the Trigger Dependent User Info field 1150 mayinclude an MPDU MU Spacing Factor subfield (2 bits), a TID AggregateLimit subfield (3 bits), a Reserved field (1 bit), and a Preferred ACsubfield (2 bits).

Hereinafter, the present disclosure proposes an example of improving acontrol field included in a PPDU. The control field improved accordingto the present disclosure includes a fist control field includingcontrol information required to interpret the PPDU and a second controlfield including control information for demodulate the data field of thePPDU. The first and second control fields may be used for variousfields. For example, the first control field may be the HE-SIG-A 730 ofFIG. 7, and the second control field may be the HE-SIG-B 740 shown inFIGS. 7 and 8.

Hereinafter, a specific example of improving the first or the secondcontrol field will be described.

In the following example, a control identifier inserted to the firstcontrol field or a second control field is proposed. The size of thecontrol identifier may vary, which, for example, may be implemented with1-bit information.

The control identifier (for example, a 1-bit identifier) may indicatewhether a 242-type RU is allocated when, for example, 20 MHztransmission is performed. As shown in FIGS. 4 to 6, RUs of varioussizes may be used. These RUs may be divided broadly into two types. Forexample, all of the RUs shown in FIGS. 4 to 6 may be classified into26-type RUs and 242-type RUs. For example, a 26-type RU may include a26-RU, a 52-RU, and a 106-RU while a 242-type RU may include a 242-RU, a484-RU, and a larger RU.

The control identifier (for example, a 1-bit identifier) may indicatethat a 242-type RU has been used. In other words, the control identifiermay indicate that a 242-RU, a 484-RU, or a 996-RU is included. If thetransmission frequency band in which a PPDU is transmitted has abandwidth of 20 MHz, a 242-RU is a single RU corresponding to the fullbandwidth of the transmission frequency band (namely, 20 MHz).Accordingly, the control identifier (for example, 1-bit identifier) mayindicate whether a single RU corresponding to the full bandwidth of thetransmission frequency band is allocated.

For example, if the transmission frequency band has a bandwidth of 40MHz, the control identifier (for example, ab 1-bit identifier) mayindicate whether a single RU corresponding to the full bandwidth(namely, bandwidth of 40 MHz) of the transmission frequency band hasbeen allocated. In other words, the control identifier may indicatewhether a 484-RU has been allocated for transmission in the frequencyband with a bandwidth of 40 MHz.

For example, if the transmission frequency band has a bandwidth of 80MHz, the control identifier (for example, a 1-bit identifier) mayindicate whether a single RU corresponding to the full bandwidth(namely, bandwidth of 80 MHz) of the transmission frequency band hasbeen allocated. In other words, the control identifier may indicatewhether a 996-RU has been allocated for transmission in the frequencyband with a bandwidth of 80 MHz.

Various technical effects may be achieved through the control identifier(for example, 1-bit identifier).

First of all, when a single RU corresponding to the full bandwidth ofthe transmission frequency band is allocated through the controlidentifier (for example, a 1-bit identifier), allocation information ofthe RU may be omitted. In other words, since only one RU rather than aplurality of RUs is allocated over the whole transmission frequencyband, allocation information of the RU may be omitted deliberately.

Also, the control identifier may be used as signaling for full bandwidthMU-MIMO. For example, when a single RU is allocated over the fullbandwidth of the transmission frequency band, multiple users may beallocated to the corresponding single RU. In other words, even thoughsignals for each user are not distinctive in the temporal and spatialdomains, other techniques (for example, spatial multiplexing) may beused to multiplex the signals for multiple users in the same, single RU.Accordingly, the control identifier (for example, a 1-bit identifier)may also be used to indicate whether to use the full bandwidth MU-MIMOdescribed above.

The common field included in the second control field (HE-SIG-B, 740)may include an RU allocation subfield. According to the PPDU bandwidth,the common field may include a plurality of RU allocation subfields(including N RU allocation subfields). The format of the common fieldmay be defined as follows.

TABLE 8 Number Subfield of bits Description RU N × 8 Indicates the RUassignment to be used in the data Allocation portion in the frequencydomain. It also indicates the number of users in each RU. For RUs ofsize greater than or equal to 106-tones that support MU-MIMO, itindicates the number of users multiplexed using MU-MIMO. Consists of NRU Allocation subfields: N = 1 for a 20 MHz and a 40 MHz HE MU PPDU N =2 for an 80 MHz HE MU PPDU N = 4 for a 160 MHz or 80 + 80 MHz HE MU PPDUCenter 1 This field is present only if(#15510) the value of 26-tone RUthe Bandwidth field of HE-SIG-A field in an HE MU PPDU is set to greaterthan 1. If the Bandwidth field of the HE-SIG-A field in an HE MU PPDU isset to 2, 4 or 5 for 80 MHz: Set to 1 to indicate that a user isallocated to the center 26-tone RU (see FIG. 28-7 (RU locations in an 80MHz HE PPDU(#16528))); otherwise, set to 0. The same value is applied toboth HE-SIG-B content channels. If the Bandwidth field of the HE-SIG-Afield in an HE MU PPDU is set to 3, 6 or 7 for 160 MHz or 80 + 80 MHz:For HE-SIG-B content channel 1, set to 1 to indicate that a user isallocated to the center 26-tone RU of the lower frequency 80 MHz;otherwise, set to 0. For HE-SIG-B content channel 2, set to 1 toindicate that a user is allocated to the center 26-tone RU of the higherfrequency 80 MHz; otherwise, set to 0. CRC 4 See 28.3.10.7.3 (CRCcomputation) Tail 6 Used to terminate the trellis of the convolutionaldecoder. Set to 0

The RU allocation subfield included in the common field of the HE-SIG-Bmay be configured with 8 bits and may indicate as follows with respectto 20 MHz PPDU bandwidth. RUs to be used as a data portion in thefrequency domain are allocated using an index for RU size anddisposition in the frequency domain. The mapping between an 8-bit RUallocation subfield for RU allocation and the number of users per RU maybe defined as follows.

TABLE 9 8 bits indices (B7 B6 B5 B4 Number B3 B2 B1 B0) #1 #2 #3 #4 #5#6 #7 #8 #9 of entries 00000000 26 26 26 26 26 26 26 26 26 1 00000001 2626 26 26 26 26 26 52 1 00000010 26 26 26 26 26 52 26 26 1 00000011 26 2626 26 26 52 52 1 00000100 26 26 52 26 26 26 26 26 1 00000101 26 26 52 2626 26 52 1 00000110 26 26 52 26 52 26 26 1 00000111 26 26 52 26 52 52 100001000 52 26 26 26 26 26 26 26 1 00001001 52 26 26 26 26 26 52 100001010 52 26 26 26 52 26 26 1 00001011 52 26 26 26 52 52 1 00001100 5252 26 26 26 26 26 1 00001101 52 52 26 26 26 52 1 00001110 52 52 26 52 2626 1 00001111 52 52 26 52 52 1 00010y₂y₁y₀ 52 52 — 106 8 00011y₂y₁y₀ 106— 52 52 8 00100y₂y₁y₀ 26 26 26 26 26 106 8 00101y₂y₁y₀ 26 26 52 26 106 800110y₂y₁y₀ 52 26 26 26 106 8 00111y₂y₁y₀ 52 52 26 106 8 01000y₂y₁y₀ 10626 26 26 26 26 8 01001y₂y₁y₀ 106 26 26 26 52 8 01010y₂y₁y₀ 106 26 52 2626 8 01011y₂y₁y₀ 106 26 52 52 8 0110y₁y₀z₁z₀ 106 — 106 16 01110000 52 52— 52 52 1 01110001 242-tone RU empty 1 01110010 484-tone RU with zeroUser fields indicated in this RU Allocation subfield of 1 the HE-SIG-Bcontent channel 01110011 996-tone RU with zero User fields indicated inthis RU Allocation subfield of 1 the HE-SIG-B content channel 011101x₁x₀Reserved 4 01111y₂y₁y₀ Reserved 8 10y₂y₁y₀z₂z₁z₀ 106 26 106 6411000y₂y₁y₀ 242 8 11001y₂y₁y₀ 484 8 11010y₂y₁y₀ 996 8 11011y₂y₁y₀Reserved 8 111x₄x₃x₂x₁x₀ Reserved 32 If (# Ed) signaling RUs of sizegreater than 242 subcarriers, y₂y₁y₀ = 000-111 indicates number of Userfields in the HE-SIG-B content channel that contains the corresponding8-bit RU Allocation subfield. Otherwise, y₂y₁y₀ = 000-111 indicatesnumber of STAs multiplexed in the 106-tone RU, 242-tone RU or the lowerfrequency 106-tone RU if there are two 106-tone RUs and one 26-tone RUis assigned between two 106-tone RUs. The binary vector y₂y₁y₀ indicates2² × y₂ + 2¹ × y₁ + y₀ + 1 STAs multiplexed the RU. z₂z₁z₀ = 000-111indicates number of STAs multiplexed in the higher frequency 106-tone RUif there are two 106-tone RUs and one 26-tone RU is assigned between two106-tone RUs. The binary vector z₂z₁z₀ indicates 2² × z₂ + 2¹ × z₁ +z₀ + 1 STAs multiplexed in the RU. Similarly, y₁y₀ = 00-11 indicatesnumber of STAs multiplexed in the lower frequency 106-tone RU. Thebinary vector y₁y₀ indicates 2¹ × y₁ + y₀ + 1 STAs multiplexed in theRU. Similarly, z₁z₀ = 00-11 indicates the number of STAs multiplexed inthe higher frequency 106-tone RU. The binary vector z₁z₀ indicates 2¹ ×z₁ + z₀ + 1 STAs multiplexed in the RU. #1 to #9 (from left to theright) is ordered in increasing order of the absolute frequency. x₁x₀ =00-11, x₄x₃x₂x₁x₀ = 00000-11111. ‘—’ means no STA in that RU.

The user-specific field included in the second control field (HE-SIG-B,740) may include a user field, a CRC field, and a Tail field. The formatof the user-specific field may be defined as follows.

TABLE 10 Number Subfield of bits Description User N × 21 The User fieldformat for a non-MU-MIMO allocation field is defined in Table 28-26(User field format for a non- MU-MIMO allocation). The User field formatfor a MU-MIMO allocation is defined in Table 28-27 (User field for anMU-MIMO allocation). N = 1 if it is the last User Block field, and ifthere is only one user in the last User Block field. N = 2 otherwise CRC4 The CRC is calculated over bits 0 to 20 for a User Block field thatcontains one User field, and bits 0 to 41 for a User Block field thatcontains two User fields. See 28.3.10.7.3 (CRC computation). Tail 6 Usedto terminate the trellis of the convolutional decoder. Set to 0.

Also, the user-specific field of the HE-SIG-B is composed of a pluralityof user fields. The plurality of user fields are located after thecommon field of the HE-SIG-B. The location of the RU allocation subfieldof the common field and that of the user field of the user-specificfield are used together to identify an RU used for transmitting data ofan STA. A plurality of RUs designated as a single STA are now allowed inthe user-specific field. Therefore, signaling that allows an STA todecode its own data is transmitted only in one user field.

As an example, it may be assumed that the RU allocation subfield isconfigured with 8 bits of 01000010 to indicate that five 26-tone RUs arearranged next to one 106-tone RU and three user fields are included inthe 106-tone RU. At this time, the 106-tone RU may support multiplexingof the three users. This example may indicate that eight user fieldsincluded in the user-specific field are mapped to six RUs, the firstthree user fields are allocated according to the MU-MIMO scheme in thefirst 106-tone RU, and the remaining five user fields are allocated toeach of the five 26-tone RUs.

A user field included in the user-specific field of the HE-SIG-B may bedefined as follows. First, the user field for non-MU-MIMO allocation isas follows.

TABLE 12 Number Bit Subfield of bits Description  B0-B10 STA-ID 11 Setto a value of the element indicated front TXVECTOR parameter STA_ID_LISE(see 27.11.1 (STA_ID_LIST)). B11-B13 NSTS 3 Number of space-timestreams. Set to the number of space-time streams minus 1. B14 Beam- 1Use of transmit beamforming. formed Set to 1 if a beamforming steeringmatrix is (#16038) applied to the waveform in an SU transmission. Set to0 otherwise. B15-B18 MCS 4 Modulation and coding scheme Set to n forMCSn, where n = 0, 1, 2, . . . , 11 Values 12 to 15 are reserved B19 DCM1 Indicates whether or not DCM is used. Set to 1 to indicate that thepayload(#Ed) of the corresponding user of the HE MU PPDU is modulatedwith DCM for the MCS. Set to 0 to indicate that the pay load of thecorresponding user of the PPDU is not modulated with DCM for the MCS.NOTE-DCM is not applied in combination with STBC. (#15664) B20 Coding 1Indicates whether BCC or LDPC is used. Set to 0 for BCC Set to 1 forLDPC NOTE- If the STA-ID subfield is set to 2046, then the othersubfields can be set to arbitrary values. (#15946)

The user field for MU-MIMO allocation is as follows.

TABLE 13 Number Bit Subfield of bits Description  B0-B10 STA-ID 11 Setto a value of element indicated from TXVECTOR parameter STA ID LIST (see27.11.1 (STA_ID_LIST)). B11-B14 Spatial 4 Indicates the number ofspatial streams for a Configuration STA in an MU-MIMO allocation (seeTable 28-28 (Spatial Configuration subfield encoding)). B15-B18 MCS 4Modulation and coding scheme. Set to n for MCSn, where n = 0, 1, 2, . .. , 11 Values 12 to 15 are reserved B19 Reserved 1 Reserved aid set to 0B20 Coding 1 Indicates whether BCC or LDPC is used. Set to 0 for BCC Setto 1 for LDPC NOTE- If the STA-ID subfield is set to 2046, then theother subfields can be set to arbitrary values. (#15946)

FIG. 12 illustrates an example of an HE TB PPDU. The PPDU of FIG. 12illustrates an uplink PPDU transmitted in response to the trigger frameof FIG. 9. At least one STA receiving a trigger frame from an AP maycheck the common information field and the individual user informationfield of the trigger frame and may transmit an HE TB PPDU simultaneouslywith another STA which has received the trigger frame.

As shown in the figure, the PPDU of FIG. 12 includes various fields,each of which corresponds to the field shown in FIGS. 2, 3, and 7.Meanwhile, as shown in the figure, the HE TB PPDU (or uplink PPDU) ofFIG. 12 may not include the HE-SIG-B field but only the HE-SIG-A field.

1. Embodiment Applicable to the Present Disclosure

The existing WiFi system uses a TDD scheme to operate DL transmission inwhich transmission is performed from an AP to an STA and UL transmissionin which transmission is performed from the STA to the AP. In this case,in order for the STA to perform UL transmission, DL reception isperformed and thereafter UL transmission is performed. Therefore, a timedelay occurs to transmit data through UL transmission. Alternatively, inorder for the AP to perform DL transmission, UL reception is performedand thereafter DL transmission is performed. Therefore, a time delayoccurs to transmit data through DL transmission.

Compared to an FDD system, a TDD system may increase frequencyefficiency because DL/UL are located at the same frequency, but has adisadvantage in that a delay is great because transmission and receptionare performed in such a manner that DL/UL are separated in terms oftime.

Meanwhile, in AR/VR, video information and user's motion informationshall be transmitted and received in an interworking manner withoutlatency. If the latency or disconnection occurs in the interworking ofthe video information and the user's motion information, an AR/VRperformance experienced by a user is significantly degraded, which leadsto a bottle neck in replacing the existing wired AR/VR with wirelesslyone.

Therefore, the proposed method proposes a method for increasing theperformance experienced by the user while replacing the AR/VR withwireless one.

The present specification proposes a series of processes and signallingto enable faster UL transmission compared to the existing wireless LANsystem. A PPDU format for support this is also proposed.

2. Proposed Embodiment

FIG. 13 is an example of applying FDD in a Wi-Fi system. That is, FDD isapplied to the existing Wi-Fi system.

In the example of FIG. 13, a DL carrier occupies 160 MHz and a ULcarrier occupies 160 MHz or 20 MHz. However, this is only an example,and thus DL and UL may occupy different bandwidths (BWs). The BW of DLand the BW of UL are not necessarily identical.

In addition, DL and UL may be located in the same band or located indifferent bands. For example, DL may be defined in a 5 GHz band, and ULmay be defined in a 2.4 GHz band. The other way around is also possible.

Meanwhile, in the proposed method, a carrier on which DL is transmittedis defined as a primary channel. It is assumed herein that DL traffic isgreater than UL traffic and an STA for performing DL transmission is anAP/PCP.

In order to operate as described above, an RF chain shall be configuredseparately for each DL and UL. In addition, in order to performtransmission and reception at the same time, two baseband modules arerequired.

FIG. 14 shows an example in which DL or UL transmission operates with aplurality of carriers in a Wi-Fi system.

In the example of FIG. 14, DL transmission is performed through twocarriers, and UL transmission is performed through one carrier. Inaddition, it is an example for a case where each of DL carriers does nothave the same BW and a UL carrier does not have the same BW, either.That is, the proposed method proposes a scheme in which each of carriersdoes not have the same BW.

Specifically, in the proposed method, a carrier having the greatest BWis selected as a primary channel. That is, secondary channels cannothave a greater BW compared to the primary channel. This is because theWi-Fi system operates a basic CCA operation by using the primarychannel. That is, the existing Wi-Fi system performs transmission byusing two channels only when the primary channel and the secondarychannel are both idle, and performs transmission by using only theprimary channel when only the secondary channel is busy. However, whenthe primary channel is busy, transmission is not possible even if thesecondary channel is idle.

In this case, if the secondary channel has a greater BW compared to theprimary channel, a throughput experienced by a user may differsignificantly according to whether the secondary channel is idle/busy.

For example, comparing a case where the BW of the primary channel isgreater than the BW of the secondary channel with the opposite case,whether the primary channel is idle/busy has the same effect on the twocases since it determines as a whole whether transmission is performed.However, according to whether the secondary channel is idle/busy, theformer case (when the BW of the primary channel is greater than the BWof the secondary channel) may perform transmission through a primarychannel occupying a wider BW, whereas the latter case (when the BW ofthe primary channel is smaller than the BW of the secondary channel)shall perform transmission through a primary channel occupying anarrower BW. Therefore, a throughput difference is great in the lattercase, compared to a case where the primary channel and the secondarychannel are both idle.

In the proposed method, two or more UL carriers may be allocated to oneDL carrier in FIG. 14. That is, 80 MHz of FIG. 14 may be used for the DLcarrier, and 40 MHz and 20 MHz of FIG. 14 may be used for the ULcarrier. This is to guarantee a UL throughput by aggregating severalchannels when a channel which can be allocated to UL is very small.

Meanwhile, when FDD is configured as shown in FIG. 13 and FIG. 14, aproblem occurs in UL channel access. That is, when an STA attemptschannel access to a UL carrier to transmit UL data, a correspondingchannel may be busy due to a co-located AP or OBSS in which the channelis used. In this case, there is a problem in that the STA cannot performUL transmission. Since this may lead to a failure in achieving thepurpose of introducing FDD to solve the low latency described above, aframe structure as shown in FIG. 15 is proposed.

FIG. 15 shows an example of a frame structure capable of transmitting aDL PPDU through a primary channel and a UL PPDU through a secondarychannel.

It is assumed in FIG. 15 that CH1 is assigned as a primary channel andused for DL, and CH2 is assigned as a secondary channel and used for UL.However, in order to solve the aforementioned problem, an APsimultaneously transmits a DL PPDU through the secondary channel. Inthis case, the DL PPDU transmitted through the secondary channel may bea preamble only frame or a Preamble+QoS null frame, or may be newlydefined to effectively operate the proposed method. In this case, thepreamble may include L-STF, L-LTF, and L-SIG, and may additionallyinclude FDD-SIG to effectively operate the proposed method. In addition,the preamble transmitted through the secondary channel is transmitted ina duplicate format such that transmission is performed in the samemanner as the preamble used in the primary channel. In doing so, whenlegacy STAs detect and decode even any one of the primary channel andthe secondary channel, it can be recognized that a corresponding channelis occupied.

In the proposed method of FIG. 15, an STA which has received the DL PPDUtransmitted through the secondary channel transmits a UL PPDU after anSIFS. Alternatively, a value other than the SIFS may be applied (e.g., avalue greater than SIFS and smaller than PIFS), and an IFS value may beindicated in a configurable manner through a beacon frame, a managementframe, and a control frame.

Although the UL PPDU of FIG. 15 may be a frame composed of only data, anACK frame for a DL PPDU received through a previous primary channel maybe aggregated with data, or it may be composed of only the ACK frame.This means that, when the ACK frame is transmitted, the ACK frame forthe primary channel is transmitted through the secondary channel. Inaddition, it means that a preamble only DL PPDU transmitted through thesecondary channel does not require ACK. In this case, the ACK frame alsoincludes a block ACK frame.

FIG. 16 shows an example of a frame structure to which FDD is appliedwhen a length of a UL PPDU is longer than a length of a DL PPDU.

Meanwhile, a maximum length of the UL PPDU is set to be equal to orshorter than an end point of the DL PPDU transmitted through a primarychannel. This is to avoid a problem in which a separate CCA operation isforced for each channel, irrespective of whether CCA is performed on aprimary channel, and thus a hardware (HW) complexity increases. This iscaused when an AP shall perform CCA on a secondary channel to transmit aDL PPDU 4 in the middle of transmitting a DL PPDU 2 in a case where theUL PPDU is longer than the DL PPDU as shown in FIG. 16.

In addition, with this configuration, since PPDUs transmitted throughthe secondary channel shall indicate length information of a UL PPDUtransmitted by STAs after an SIFS, there is a problem in that theaforementioned preamble only DL PPDU structure cannot be used. That is,since a preamble of PPDUs transmitted through the secondary channel iscomposed of a duplicate format of a preamble transmitted through theprimary channel, L-SIG information indicates a length of a PPDUtransmitted through the primary channel, and a MAC frame shall beincluded to guarantee up to the UL PPDU.

In the proposed method, BW information of the primary channel andsecondary channel may be indicated by FDD-SIG which is newly defined.Alternatively, it may be indicated through request to send (RTS) andclear to send (CTS) frames as shown in FIG. 17. The RTS frame and theCTS frame are signaling frames for solving a hidden node problem and anexposed node problem, and a wireless device may overhear whether data istransmitted and received between neighboring STAs, based on the RTSframe and the CTS frame.

FIG. 17 is an example of a frame structure to which FDD is applied byusing an RTS frame and a CTS frame.

In case of FIG. 17, a center frequency or a channel number and BWinformation may be included in the RTS and CTS frames, and a new framemay be configured for indication.

FIG. 18 is another example of a frame structure to which FDD is appliedby using an RTS frame and a CTS frame.

In addition, if the RTS frame uses 1 bit to indicate that a UL frame istransmitted in a corresponding channel, a UL PPDU may be immediatelytransmitted after an SIFS of CRS without transmission or assistance of aDL PPDU in a secondary channel. An embodiment for this is shown in FIG.18.

FIG. 19 and FIG. 20 are examples of a frame structure to which FDD isapplied by using a trigger frame.

FIG. 19 is an embodiment in which two STAs use CH#1 and CH#4 to performFDD transmission, and FIG. 20 is an embodiment in which three STAs useCH#1, CH#5, and CH#4 to perform FDD transmission.

Referring to FIG. 19 and FIG. 20, transmission may be performed by usingthe trigger frame without having to use an RTS/CTS frame.

In FIG. 19 and FIG. 20, the trigger frame may include a centerfrequency, a channel number, a BW, a DL/UL indication, a DL/UL PPDUduration, or DL/UL TXOP duration information. In addition, a method ofconfiguring a DL PPDU and a UL PPDU in terms of time in a correspondingchannel may be included for flexibility of a time resource, so thatDL/UL can be freely changed in each channel. In this case, although atrigger frame transmitted through each channel may be transmitted byincluding only information on each channel as shown in FIG. 19, it isalso possible that the trigger frame is configured by using informationon all channels and may be transmitted by using a duplicate format, sothat configuration information on all channels can be recognized even ifonly any one of the channels is received.

However, there is a case where a data part (PSDU) included in a DL PPDUof CH#4 is transmitted by being aggregated with a trigger frame of CH#4.If so, a DL PPDU may be transmitted by being included in a trigger framein CH#4 of FIG. 19 and FIG. 20, and a UL PPDU may be transmitted when anSIFS elapses after the trigger frame is received. In this case, however,a trigger frame for each channel shall be configured independentlywithout having to use a duplicate format.

Hereinafter, the aforementioned embodiment is described over time withreference to FIG. 20.

FIG. 21 shows a procedure in which a PPDU is transmitted based on FDDaccording to the present embodiment.

It is assumed in the embodiment of FIG. 21 that an AP supports an FDDscheme, and an STA supports a multi-band and the FDD scheme.

Referring to FIG. 21, the AP transmits a trigger frame to an STA1 to anSTA3. The trigger frame includes bandwidth information of a primarychannel and secondary channel and scheduling information of the STA1 toSTA3.

The STA1 decodes the trigger frame to identify that the STA1 receives aDL PPDU by using the primary channel and FDD is applied thereto. Indoing so, the STA1 may receive the DL PPDU from the AP through theprimary channel.

The STA2 decodes the trigger frame to identify that the STA2 receivesthe DL PPDU by using the secondary channel and FDD is applied thereto.Likewise, the STA2 may receive the DL PPDU from the AP and transmit theUL PPDU to the AP after an SIFS. That is, by being divided in a timedomain, the DL PPDU is first received through the secondary channel, andthereafter the UL PPDU is transmitted.

The STA3 may decode the trigger frame to identify that the STA3transmits the UL PPDU by using another secondary channel and FDD isapplied thereto. In doing so, the STA3 may transmit the UL PPDU assignedthereto in another secondary channel to the AP. According to FIG. 21,the PPDU transmitted and received by the first to third STAs may besimultaneously transmitted in different frequency bands.

The FDD-based PPDU transmission will be described below in detail withreference to FIG. 22 and FIG. 23.

FIG. 22 is a flowchart illustrating a procedure in which a PPDU istransmitted and received based on FDD from an AP perspective accordingto the present embodiment.

An example of FIG. 22 may be performed in a network environment in whicha next-generation WLAN system is supported. The next-generation WLANsystem is a WLAN system evolved from an 802.11ax system, and may satisfybackward compatibility with the 802.11ax system.

The example of FIG. 22 may be performed in a transmitting device, andthe transmitting device may correspond to an AP. A receiving device ofFIG. 22 may correspond to an STA (non-AP STA) having FDD capability.

In step S2210, the AP transmits a trigger frame to a first STA and asecond STA.

In step S2220, the AP transmits a first DL PPDU to the first STA, basedon the trigger frame.

In step S2230, the AP transmits a second DL PPDU to the second STA,based on the trigger frame.

In step S2240, the AP receives a first UL PPDU from the second STA,based on the trigger frame.

The trigger frame includes bandwidth information of a primary channeland secondary channel.

The first DL PPDU is transmitted through the primary channel, and thesecond DL PPDU and the first UL PPDU are transmitted through thesecondary channel.

The first and second DL PPDUs are simultaneously transmitted. The firstDL PPDU and the second DL PPDU may have the same transmission starttime, but a transmission end time may be different from each other.

The first UL PPDU is received when a pre-set duration elapses after thesecond DL PPDU is transmitted. That is, the first UL PPDU and the secondDL PPDU are identical in a frequency domain, and may be identified in atime domain.

The trigger frame, the first DL and second DL PPDUs, and the first ULPPDU may be a frame or PPDU used in the 802.11ax system, or may be newlydefined in the next-generation WLAN system.

The first DL PPDU may include a first preamble and a first data field.The second DL PPDU may include only a second preamble, or may includethe second preamble and a quality of service (QoS) null frame.

The second preamble may be a preamble obtained by duplicating the firstpreamble.

The second preamble may include a legacy-short training field (L-STF), alegacy-long training field (L-LTF), a legacy-signal (L-SIG), and anFDD-signal (FDD-SIG). The FDD-SIG may include bandwidth information ofthe primary channel and secondary channel.

The pre-set duration may be set to a first duration or a secondduration. The first duration may be a short inter-frame space (SIFS),and the second duration may be a duration having a value greater thanthe SIFS and less than a point coordination function inter-frame space(PIFS).

The first UL PPDU may include only a second data field, or may includeonly an ACK frame for the first DL PPDU, or may include a frame obtainedby aggregating the second data field and the ACK frame. The ACK framemay include a block Ack (BA) frame.

The first UL PPDU may not include an ACK frame for the second DL PPDU.In practice, the ACK frame for the second DL PPDU is not required.

A transmission end time of the first UL PPDU may be equal or prior to atransmission end time of the first DL PPDU. The L-SIG may includeinformation on the transmission end time of the first DL PPDU.

The trigger frame may further include information on a center frame, achannel number of the primary channel and secondary channel, indicationinformation of DL and UL PPDUs, duration information of the DL and ULPPDUs, and transmission opportunity (TXOP) information of the DL and ULPPDUs.

The trigger frame may include a first trigger frame transmitted in theprimary channel and a second trigger frame transmitted in the secondarychannel.

The second trigger frame may be obtained by duplicating the firsttrigger frame.

If the second trigger frame is aggregated with a physical layer servicedata unit (PSDU) included in the second DL PPDU, the first UL PPDU maybe received when an SIFS elapses after the trigger frame is transmitted.In this case, the second trigger frame may be composed of independenttrigger frames, instead of duplicating the first trigger frame.

FIG. 23 is a flowchart illustrating a procedure in which a PPDU istransmitted and received based on FDD from an STA perspective accordingto the present embodiment.

An example of FIG. 23 may be performed in a network environment in whicha next-generation WLAN system is supported. The next-generation WLANsystem is a WLAN system evolved from an 802.11ax system, and may satisfybackward compatibility with the 802.11ax system.

The example of FIG. 23 may be performed in a receiving device, and thereceiving device may correspond to an STA (non-AP STA) having FDDcapability. A transmitting device of FIG. 23 may correspond to an AP.

In step S2310, a second STA receives a trigger frame from the AP.

In step S2320, the second STA receives a second DL PPDU from the AP,based on the trigger frame.

In step S2330, the second STA transmits a first UL PPDU to the AP, basedon the trigger frame.

In this case, the trigger frame is received by a first STA from the AP,and the first DL PPDU is received by the first STA, based on the triggerframe.

The trigger frame includes bandwidth information of a primary channeland secondary channel.

The first DL PPDU is transmitted through the primary channel, and thesecond DL PPDU and the first UL PPDU are transmitted through thesecondary channel.

The first and second DL PPDUs are simultaneously transmitted. The firstDL PPDU and the second DL PPDU may have the same transmission starttime, but a transmission end time may be different from each other.

The first UL PPDU is received when a pre-set duration elapses after thesecond DL PPDU is transmitted. That is, the first UL PPDU and the secondDL PPDU are identical in a frequency domain, and may be identified in atime domain.

The trigger frame, the first DL and second DL PPDUs, and the first ULPPDU may be a frame or PPDU used in the 802.11ax system, or may be newlydefined in the next-generation WLAN system.

The first DL PPDU may include a first preamble and a first data field.The second DL PPDU may include only a second preamble, or may includethe second preamble and a quality of service (QoS) null frame.

The second preamble may be a preamble obtained by duplicating the firstpreamble.

The second preamble may include a legacy-short training field (L-STF), alegacy-long training field (L-LTF), a legacy-signal (L-SIG), and anFDD-signal (FDD-SIG). The FDD-SIG may include bandwidth information ofthe primary channel and secondary channel.

The pre-set duration may be set to a first duration or a secondduration. The first duration may be a short inter-frame space (SIFS),and the second duration may be a duration having a value greater thanthe SIFS and less than a point coordination function inter-frame space(PIFS).

The first UL PPDU may include only a second data field, or may includeonly an ACK frame for the first DL PPDU, or may include a frame obtainedby aggregating the second data field and the ACK frame. The ACK framemay include a block Ack (BA) frame.

The first UL PPDU may not include an ACK frame for the second DL PPDU.In practice, the ACK frame for the second DL PPDU is not required.

A transmission end time of the first UL PPDU may be equal or prior to atransmission end time of the first DL PPDU. The L-SIG may includeinformation on the transmission end time of the first DL PPDU.

The trigger frame may further include information on a center frame, achannel number of the primary channel and secondary channel, indicationinformation of DL and UL PPDUs, duration information of the DL and ULPPDUs, and transmission opportunity (TXOP) information of the DL and ULPPDUs.

The trigger frame may include a first trigger frame transmitted in theprimary channel and a second trigger frame transmitted in the secondarychannel.

The second trigger frame may be obtained by duplicating the firsttrigger frame.

If the second trigger frame is aggregated with a physical layer servicedata unit (PSDU) included in the second DL PPDU, the first UL PPDU maybe received when an SIFS elapses after the trigger frame is transmitted.In this case, the second trigger frame may be composed of independenttrigger frames, instead of duplicating the first trigger frame.

3. Device Configuration

FIG. 24 is a diagram illustrating a device for implementing theaforementioned method.

A wireless device 100 of FIG. 24 is a transmission device capable ofimplementing the aforementioned embodiment, and may operate as an APSTA. A wireless device 150 of FIG. 24 is a receiving device capable ofimplementing the aforementioned embodiment, and may operate as a non-APSTA.

The transmitting device (100) may include a processor (110), a memory(120), and a transmitting/receiving unit (130), and the receiving device(150) may include a processor (160), a memory (170), and atransmitting/receiving unit (180). The transmitting/receiving unit (130,180) transmits/receives a radio signal and may be operated in a physicallayer of IEEE 802.11/3GPP, and so on. The processor (110, 160) may beoperated in the physical layer and/or MAC layer and may be operativelyconnected to the transmitting/receiving unit (130, 180).

The processor (110, 160) and/or the transmitting/receiving unit (130,180) may include application-specific integrated circuit (ASIC), otherchipset, logic circuit and/or data processor. The memory (120, 170) mayinclude read-only memory (ROM), random access memory (RAM), flashmemory, memory card, storage medium and/or other storage unit. When theembodiments are executed by software, the techniques (or methods)described herein can be executed with modules (e.g., processes,functions, and so on) that perform the functions described herein. Themodules can be stored in the memory (120, 170) and executed by theprocessor (110, 160). The memory (120, 170) can be implemented (orpositioned) within the processor (110, 160) or external to the processor(110, 160). Also, the memory (120, 170) may be operatively connected tothe processor (110, 160) via various means known in the art.

The processor 110, 160 may implement the functions, processes and/ormethods proposed in the present disclosure. For example, the processor110, 160 may perform the operation according to the present embodiment.

An operation of the processor 110 of the transmitting device isdescribed in detail as follows. The processor 110 of the transmittingdevice transmits a trigger frame to a first STA and a second STA, andtransmits and receives a first DL PPDU, a second DL PPDU, a first ULPPDU to and from the first STA and the second STA, based on the triggerframe.

An operation of the processor 160 of the receiving device is describedin detail as follows. The processor 160 of the receiving device receivesa trigger frame from the AP, and transmits and receives a first DL PPDU,a second DL PPDU, and a first UL PPDU to and from the AP, based on thetrigger frame.

FIG. 25 shows more detailed wireless device to implement an embodimentof the present disclosure. The present disclosure described above forthe transmitting device or the receiving device may be applied to thisembodiment.

A wireless device includes a processor 610, a power management module611, a battery 612, a display 613, a keypad 614, a subscriberidentification module (SIM) card 615, a memory 620, a transceiver 630,one or more antennas 631, a speaker 640, and a microphone 641.

The processor 610 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 610. Theprocessor 610 may include ASIC, other chipset, logic circuit and/or dataprocessing device. The processor 610 may be an application processor(AP). The processor 610 may include at least one of a digital signalprocessor (DSP), a central processing unit (CPU), a graphics processingunit (GPU), a modem (modulator and demodulator). An example of theprocessor 610 may be found in SNAPDRAGON™ series of processors made byQualcomm®, EXYNOS® series of processors made by Samsung®, A series ofprocessors made by Apple®, HELIO™ series of processors made byMediaTek®, ATOM™ series of processors made by Intel® or a correspondingnext generation processor.

The power management module 611 manages power for the processor 610and/or the transceiver 630. The battery 612 supplies power to the powermanagement module 611. The display 613 outputs results processed by theprocessor 610. The keypad 614 receives inputs to be used by theprocessor 610. The keypad 614 may be shown on the display 613. The SIMcard 615 is an integrated circuit that is intended to securely store theinternational mobile subscriber identity (IMSI) number and its relatedkey, which are used to identify and authenticate subscribers on mobiletelephony devices (such as mobile phones and computers). It is alsopossible to store contact information on many SIM cards.

The memory 620 is operatively coupled with the processor 610 and storesa variety of information to operate the processor 610. The memory 620may include ROM, RAM, flash memory, memory card, storage medium and/orother storage device. When the embodiments are implemented in software,the techniques described herein can be implemented with modules (e.g.,procedures, functions, and so on) that perform the functions describedherein. The modules can be stored in the memory 620 and executed by theprocessor 610. The memory 620 can be implemented within the processor610 or external to the processor 610 in which case those can becommunicatively coupled to the processor 610 via various means as isknown in the art.

The transceiver 630 is operatively coupled with the processor 610, andtransmits and/or receives a radio signal. The transceiver 630 includes atransmitter and a receiver. The transceiver 630 may include basebandcircuitry to process radio frequency signals. The transceiver 630controls the one or more antennas 631 to transmit and/or receive a radiosignal.

The speaker 640 outputs sound-related results processed by the processor610. The microphone 641 receives sound-related inputs to be used by theprocessor 610.

In case of the transmitting device, the processor 610 transmits atrigger frame to a first STA and a second STA, and transmits andreceives a first DL PPDU, a second DL PPDU, a first UL PPDU to and fromthe first STA and the second STA, based on the trigger frame.

In case of the receiving device, the processor 610 receives a triggerframe from the AP, and transmits and receives a first DL PPDU, a secondDL PPDU, and a first UL PPDU to and from the AP, based on the triggerframe.

The trigger frame includes bandwidth information of a primary channeland secondary channel.

The first DL PPDU is transmitted through the primary channel, and thesecond DL PPDU and the first UL PPDU are transmitted through thesecondary channel.

The first and second DL PPDUs are simultaneously transmitted. The firstDL PPDU and the second DL PPDU may have the same transmission starttime, but a transmission end time may be different from each other.

The first UL PPDU is received when a pre-set duration elapses after thesecond DL PPDU is transmitted. That is, the first UL PPDU and the secondDL PPDU are identical in a frequency domain, and may be identified in atime domain.

The trigger frame, the first DL and second DL PPDUs, and the first ULPPDU may be a frame or PPDU used in the 802.11ax system, or may be newlydefined in the next-generation WLAN system.

The first DL PPDU may include a first preamble and a first data field.The second DL PPDU may include only a second preamble, or may includethe second preamble and a quality of service (QoS) null frame.

The second preamble may be a preamble obtained by duplicating the firstpreamble.

The second preamble may include a legacy-short training field (L-STF), alegacy-long training field (L-LTF), a legacy-signal (L-SIG), and anFDD-signal (FDD-SIG). The FDD-SIG may include bandwidth information ofthe primary channel and secondary channel.

The pre-set duration may be set to a first duration or a secondduration. The first duration may be a short inter-frame space (SIFS),and the second duration may be a duration having a value greater thanthe SIFS and less than a point coordination function inter-frame space(PIFS).

The first UL PPDU may include only a second data field, or may includeonly an ACK frame for the first DL PPDU, or may include a frame obtainedby aggregating the second data field and the ACK frame. The ACK framemay include a block Ack (BA) frame.

The first UL PPDU may not include an ACK frame for the second DL PPDU.In practice, the ACK frame for the second DL PPDU is not required.

A transmission end time of the first UL PPDU may be equal or prior to atransmission end time of the first DL PPDU. The L-SIG may includeinformation on the transmission end time of the first DL PPDU.

The trigger frame may further include information on a center frame, achannel number of the primary channel and secondary channel, indicationinformation of DL and UL PPDUs, duration information of the DL and ULPPDUs, and transmission opportunity (TXOP) information of the DL and ULPPDUs.

The trigger frame may include a first trigger frame transmitted in theprimary channel and a second trigger frame transmitted in the secondarychannel.

The second trigger frame may be obtained by duplicating the firsttrigger frame.

If the second trigger frame is aggregated with a physical layer servicedata unit (PSDU) included in the second DL PPDU, the first UL PPDU maybe received when an SIFS elapses after the trigger frame is transmitted.In this case, the second trigger frame may be composed of independenttrigger frames, instead of duplicating the first trigger frame.

What is claimed is:
 1. A method in a wireless local area network (WLAN)system, the method comprising: transmitting, by an access point (AP)supporting a primary channel and a secondary channel, a first downlink(DL) PPDU to a first STA; and receiving, by the AP, a first uplink (UL)PPDU from a second STA, wherein the first DL PPDU is transmitted throughthe primary channel while the first UL PPDU is received through thesecondary channel.
 2. The method of claim 1, further comprising:transmitting, by the AP, a second DL PPDU to the second STA, wherein thefirst DL PPDU comprises a first preamble and a first data field, whereinthe second DL PPDU comprises only a second preamble or comprises thesecond preamble and a quality of service (QoS) null frame, and whereinthe second preamble is a preamble obtained by duplicating the firstpreamble.
 3. The method of claim 2, wherein the second preamblecomprises a legacy-short training field (L-STF), a legacy-long trainingfield (L-LTF), a legacy-signal (L-SIG), and an FDD-signal (FDD-SIG), andwherein the FDD-SIG comprises bandwidth information of the primarychannel and secondary channel.
 4. The method of claim 1, wherein thepre-set duration is set to a first duration or a second duration,wherein the first duration is a short inter-frame space (SIFS), andwherein the second duration is a duration having a value greater thanthe SIFS and less than a point coordination function inter-frame space(PIFS).
 5. The method of claim 1, wherein the first UL PPDU comprisesonly a second data field, or comprises only an ACK frame for the firstDL PPDU, or comprises a frame obtained by aggregating the second datafield and the ACK frame, and wherein the ACK frame comprises a block Ack(BA) frame.
 6. The method of claim 5, wherein the first UL PPDU does notinclude an ACK frame for the second DL PPDU, and wherein the ACK framefor the second DL PPDU is not required.
 7. The method of claim 3,wherein a transmission end time of the first UL PPDU is equal or priorto a transmission end time of the first DL PPDU, and wherein the L-SIGcomprises information on the transmission end time of the first DL PPDU.8. The method of claim 1, further comprising: transmitting, by the AP, atrigger frame to the first STA and the second STA, wherein the triggerframe comprises bandwidth information of the primary channel and thesecondary channel, information on a center frame, a channel number ofthe primary channel and secondary channel, indication information of DLand UL PPDUs, duration information of the DL and UL PPDUs, andtransmission opportunity (TXOP) information of the DL and UL PPDUs, andwherein the trigger frame further comprises a first trigger frametransmitted in the primary channel and a second trigger frametransmitted in the secondary channel.
 9. The method of claim 8, whereinthe second trigger frame is obtained by duplicating the first triggerframe.
 10. The method of claim 8, wherein if the second trigger frame isaggregated with a physical layer service data unit (PSDU) comprised inthe second DL PPDU, the first UL PPDU is received when an SIFS elapsesafter the trigger frame is transmitted.
 11. An access point (AP)supporting a primary channel and a secondary channel in a wireless localarea network (WLAN) system, the AP comprising: a memory; a transceiver;and a processor operatively coupled to the memory and the transceiver,wherein the processor is configured to: transmit a first downlink (DL)PPDU to a first STA; and receive a first uplink (UL) PPDU from a secondSTA, wherein the first DL PPDU is transmitted through the primarychannel while the first UL PPDU is received through the secondarychannel.
 12. The wireless device of claim 11, wherein the processor isfurther configured to: transmit a second DL PPDU to the second STA,wherein the first DL PPDU comprises a first preamble and a first datafield, wherein the second DL PPDU comprises only a second preamble orcomprises the second preamble and a quality of service (QoS) null frame,and wherein the second preamble is a preamble obtained by duplicatingthe first preamble.
 13. The wireless device of claim 12, wherein thesecond preamble comprises a legacy-short training field (L-STF), alegacy-long training field (L-LTF), a legacy-signal (L-SIG), and anFDD-signal (FDD-SIG), and wherein the FDD-SIG comprises bandwidthinformation of the primary channel and secondary channel.
 14. Thewireless device of claim 11, wherein the pre-set duration is set to afirst duration or a second duration, wherein the first duration is ashort inter-frame space (SIFS), and wherein the second duration is aduration having a value greater than the SIFS and less than a pointcoordination function inter-frame space (PIFS).
 15. The wireless deviceof claim 11, wherein the first UL PPDU comprises only a second datafield, or comprises only an ACK frame for the first DL PPDU, orcomprises a frame obtained by aggregating the second data field and theACK frame, and wherein the ACK frame comprises a block Ack (BA) frame.16. The wireless device of claim 15, wherein the first UL PPDU does notinclude an ACK frame for the second DL PPDU, and wherein the ACK framefor the second DL PPDU is not required.
 17. The wireless device of claim13, wherein a transmission end time of the first UL PPDU is equal orprior to a transmission end time of the first DL PPDU, and wherein theL-SIG comprises information on the transmission end time of the first DLPPDU.
 18. The wireless device of claim 11, wherein the processor isfurther configured to: transmit a trigger frame to the first STA and thesecond STA, wherein the trigger frame further comprises bandwidthinformation of the primary channel and the secondary channel,information on a center frame, a channel number of the primary channeland secondary channel, indication information of DL and UL PPDUs,duration information of the DL and UL PPDUs, and transmissionopportunity (TXOP) information of the DL and UL PPDUs, and wherein thetrigger frame further comprises a first trigger frame transmitted in theprimary channel and a second trigger frame transmitted in the secondarychannel.
 19. The wireless device of claim 18, wherein the second triggerframe is obtained by duplicating the first trigger frame.